As filed with the Securities and Exchange Commission on July 2, 2018

Registration No. 333-225521

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

PRE-EFFECTIVE AMENDMENT NO. 1

TO THE

FORM S-4

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

FIRST INTERSTATE BANCSYSTEM, INC.

(Exact name of registrant as specified in its charter)

401 North 31st Street

Billings, Montana 59116

(406) 255-5390

(Address, Including Zip Code, and Telephone Number, Including Area Code, of Registrant’s Principal Executive Offices)

Kevin P. Riley

President and Chief Executive Officer

401 North 31st Street

Billings, Montana 59116

(406) 255-5390

(Address, Including Zip Code, and Telephone Number, Including Area Code, of Agent for Service)

Copies to:

Approximate date of commencement of proposed sale to the public: As soon as practicable after this registration statement becomes effective and upon completion of the merger.

If the securities being registered on this Form are being offered in connection with the formation of a holding company and there is compliance with General Instruction G, check the following box:  ☐

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act.  ☐

If applicable, place an X in the box to designate the appropriate rule provision relied upon in conducting this transaction:

Exchange Act Rule 13e-4(i) (Cross-Border Issuer Tender Offer)  ☐

Exchange Act Rule 14d-1(d) (Cross-Border Third-Party Tender Offer)  ☐

CALCULATION OF REGISTRATION FEE

The Registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

Information contained in this proxy statement/prospectus is subject to completion or amendment. A registration statement relating to the shares of First Interstate BancSystem, Inc. Class A common stock to be issued in the merger has been filed with the Securities and Exchange Commission. These securities may not be sold nor may offers to buy be accepted before the time the registration statement becomes effective. This proxy statement/prospectus shall not constitute an offer to sell or the solicitation of an offer to buy nor shall there be any sale of these securities in any jurisdiction in which such offer, solicitation or sale is not permitted or would be unlawful before registration or qualification under the securities laws of any such jurisdiction.

PRELIMINARY PROXY STATEMENT/PROSPECTUS,

SUBJECT TO COMPLETION, DATED JULY 2, 2018

MERGER PROPOSED—YOUR VOTE IS VERY IMPORTANT

Dear Northwest Bancorporation, Inc. Shareholder:

On April 25, 2018, First Interstate BancSystem, Inc. (which we refer to as “First Interstate”) and Northwest Bancorporation, Inc. (which we refer to as “Northwest”) entered into an Agreement and Plan of Merger (which we refer to as the “merger agreement”) under which Northwest will merge with and into First Interstate, with First Interstate remaining as the surviving entity. This transaction is referred to in this document as the “merger.” Following the merger, Inland Northwest Bank, the wholly-owned subsidiary of Northwest, will merge with and into First Interstate Bank, the wholly-owned subsidiary of First Interstate, with First Interstate Bank as the surviving entity. This transaction is referred to in this document as the “bank merger.” Before we complete the merger, the shareholders of Northwest must approve the merger agreement.

If the merger is completed, Northwest shareholders will be entitled to receive, for each share of Northwest common stock they own, 0.516 shares of First Interstate Class A common stock. The maximum number of shares of First Interstate Class A common stock estimated to be issuable upon completion of the merger is 3,982,842. Based on First Interstate’s closing price of $40.10 on April 25, 2018, which was the last trading date preceding the public announcement of the proposed merger, each share of Northwest common stock exchanged for 0.516 shares of First Interstate Class A common stock would have a value of $20.69, or approximately $159.7 million in the aggregate. Based on First Interstate’s closing price of $42.40 on June 27, 2018, which is the most recent practicable trading day before the printing of this document, each share of Northwest common stock exchanged for 0.516 shares of First Interstate Class A common stock would have a value of $21.88. The common stock of First Interstate trades on the Nasdaq Global Select Market under the symbol “FIBK.” The common stock of Northwest is quoted on the OTC Market’s Pink Marketplace under the symbol “NBCT.” The market price of both First Interstate Class A common stock and Northwest common stock will fluctuate before the completion of the merger; therefore, you are urged to obtain current market quotations for First Interstate Class A common stock and Northwest common stock.

Although the number of shares of First Interstate Class A common stock that holders of Northwest common stock will be entitled to receive is fixed, the market value of the stock consideration will fluctuate with the market price of First Interstate Class A common stock and will not be known at the time Northwest shareholders vote on the merger. However, Northwest has the right to terminate the merger agreement if, at any time during a five-day period commencing on the fifth day before closing, the average closing price of First Interstate Class A common stock over the 20 consecutive trading days ending on and including the fifth day before closing (1) is less than $32.00 and (2) underperforms the KBW Regional Banking Index by more than 20% during the same time period. If Northwest elects to exercise this termination right, then First Interstate has the option to increase the exchange ratio to a level that would eliminate the effects of the two requirements of this termination right.

The affirmative vote of two-thirds of the outstanding shares of Northwest common stock is required to approve the merger agreement. Northwest shareholders will vote to adopt the merger agreement at a special meeting of shareholders to be held at 5:00 p.m., local time, on August 14, 2018 at the Airway Heights branch of Inland Northwest Bank located at 11917 West Sunset Highway, Airway Heights, Washington.

Northwest’s board of directors unanimously recommends that Northwest shareholders vote “FOR” the adoption of the merger agreement.

This document contains information that you should consider in evaluating the proposed merger. In particular, you should carefully read the section captioned “Risk Factors” beginning on page 14 for a discussion of certain risk factors relating to the merger. You can also obtain information about First Interstate from documents filed with the Securities and Exchange Commission.

We look forward to seeing you at the shareholders meeting and we appreciate your continued support.

Russell A. Lee

President and Chief Executive Officer

Northwest Bancorporation, Inc.

The shares of First Interstate Class A common stock to be issued in the merger are not deposits or savings accounts or other obligations of any bank or savings association and are not insured by the FDIC or any other governmental agency.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved the merger described in this document or the First Interstate Class A common stock to be issued in the merger, or passed upon the adequacy or accuracy of this document. Any representation to the contrary is a criminal offense.

The date of this proxy statement/prospectus is [●], 2018, and it is first being mailed or otherwise delivered to shareholders of Northwest on or about [●], 2018.

ABOUT THIS DOCUMENT

This proxy statement/prospectus, which we refer to as “this document,” which forms part of a registration statement on Form S-4 filed with the Securities and Exchange Commission (which we refer to as the “SEC”) by First Interstate, constitutes a prospectus of First Interstate with respect to the shares of First Interstate Class A common stock to be issued to Northwest shareholders, as required by the merger agreement. This document also constitutes a proxy statement and a notice of meeting with respect to the special meeting of shareholders of Northwest.

You should rely only on the information contained in this document. No one has been authorized to provide you with information that is different from the information contained in this document. This document is dated [●], 2018. You should not assume that the information contained in this document is accurate as of any date other than that date. Neither the mailing of this document to Northwest shareholders nor the issuance by First Interstate of its common stock in connection with the merger will create any implication to the contrary.

This document does not constitute an offer to sell, or a solicitation of an offer to buy, any securities, or the solicitation of a proxy, in any jurisdiction to or from any person to whom it is unlawful to make any such offer or solicitation in such jurisdiction. Information contained in this document regarding First Interstate has been provided by First Interstate and information contained in this document regarding Northwest has been provided by Northwest.

NORTHWEST BANCORPORATION, INC.

421 West Riverside Avenue, Suite 113

Spokane, Washington 99201

Notice of Special Meeting of Shareholders to be held August 14, 2018

To the Shareholders of Northwest:

Northwest will hold a special meeting of shareholders (which we refer to as the “Northwest special meeting”) at 5:00 p.m., local time, on August 14, 2018, at the Airway Heights Branch of Inland Northwest Bank located at 11917 West Sunset Highway, Airway Heights, Washington, to consider and vote on the following matters:

Both of these items are described in more detail in the accompanying proxy statement/prospectus and its annexes. We urge you to read these materials carefully and in their entirety. The enclosed document forms a part of this notice.

Northwest’s board of directors unanimously recommends that Northwest shareholders vote “FOR” both of the proposals.

Northwest shareholders of record as of the close of business on June 27, 2018 are entitled to notice of, and to vote at, the Northwest special meeting and any adjournments or postponements of the Northwest special meeting.

Northwest shareholders have the right to dissent from the merger and obtain payment of the cash appraisal fair value of their Northwest shares under applicable provisions of Washington law. A copy of the provisions regarding dissenters’ rights is attached as Annex B to the accompanying proxy statement/prospectus. For details of your dissenter’s rights and how to exercise them, please see the discussion under “Description of the Merger—Dissenters’ Rights of Appraisal.”

Your vote is very important. Your proxy is being solicited by Northwest’s board of directors. For the proposed merger to be completed, the proposal to approve the merger agreement must be approved by the affirmative vote of two-thirds of the outstanding shares of Northwest common stock. The Northwest adjournment proposal will be approved if a majority of the votes cast on such proposal at the Northwest special meeting are voted in favor of such proposal.

Whether or not you plan to attend the Northwest special meeting, we urge you to vote. Shareholders of record may vote:

If you hold your stock in “street name” through a banker or broker, please follow the instructions on the voting instruction card furnished by the record holder.

If you have any questions or need assistance voting your shares, please contact our proxy solicitor, Laurel Hill Advisory Group, toll free at (888) 742-1305.

By Order of the Board of Directors,

Leilani T. McKernan

Corporate Secretary

Spokane, Washington

[●], 2018

REFERENCES TO AVAILABLE INFORMATION

This document incorporates important business and financial information about First Interstate from documents filed with the SEC that have not been included in or delivered with this document. You may read and copy these documents at the SEC’s public reference room located at 100 F Street, NE, Washington, DC 20549. Copies of these documents also can be obtained at prescribed rates by writing to the Public Reference Section of the SEC, at 100 F Street, NE, Washington, DC 20549 or by calling 1-800-SEC-0330 for additional information on the operation of the public reference facilities. This information is also available at the Internet site the SEC maintains at http://www.sec.gov. See “Where You Can Find More Information” on page 93.

You also may request orally or in writing copies of these documents at no cost by contacting First Interstate at the following address:

First Interstate BancSystem, Inc.

401 North 31^st Street

Billings, Montana 59101

Attention: Kirk D. Jensen, General Counsel

Telephone: (406) 255-5304

If you are a Northwest shareholder and would like to request documents from First Interstate, please do so by August 7, 2018 to receive them before the Northwest special meeting.

TABLE OF CONTENTS

QUESTIONS AND ANSWERS ABOUT THE MERGER AND THE NORTHWEST SPECIAL MEETING

The following are answers to certain questions that you may have regarding the merger and the Northwest special meeting. We urge you to read carefully the remainder of this document because the information in this section may not provide all the information that might be important to you in determining how to vote. Additional important information is also contained in the annexes to, and the documents incorporated by reference in this document.

To approve the merger agreement, Northwest has called a special meeting of its shareholders (which we refer to as the “Northwest special meeting”). This document also serves as a notice of the Northwest special meeting, and describes the proposals to be presented at the Northwest special meeting.

You should read this document carefully and in its entirety. The enclosed materials allow you to have your shares voted by proxy without attending your special meeting. Your vote is important. We encourage you to submit your proxy as soon as possible.

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Stock Purchase Warrants: At the effective time of the merger, each warrant to purchase shares of Northwest common stock outstanding immediately before the effective time of the merger, whether or not vested, will be canceled and, upon First Interstate’s receipt of a warrant termination agreement from the holder, exchanged for a cash payment equal to the product of (1) the number of shares of Northwest common stock subject to the warrant multiplied by (2) the amount by which the product of the average closing price and the exchange ratio exceeds the exercise price of such warrant, less applicable withholding taxes.

Restricted Stock Awards: At the effective time of the merger, each outstanding share of restricted stock will vest and be converted into the right to receive 0.516 shares of First Interstate Class A common stock.

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Approval of the Northwest adjournment proposal requires that the votes cast in favor of the proposal exceed the votes cast against. Abstentions and broker non-votes will not affect the outcome of the Northwest adjournment proposal.

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Please refer to the specific instructions set forth on the proxy card. We encourage you to vote via the internet or by telephone.

If you hold your shares of Northwest common stock in “street name” through a bank or broker, you should contact your bank or broker to change your vote or revoke your proxy.

Your last vote will be the vote that is counted.

If your shares are held in “street name,” you must vote your shares according to the voting instructions form by the deadline set by your broker, bank or other nominee.

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You should read “Description of the Merger—Material U.S. Federal Income Tax Consequences of the Merger” beginning on page 56 of this document for more information about the United States federal income tax consequences of the merger. Tax matters can be complicated and the tax consequences of the merger will depend on your particular tax situation. You should consult your tax advisor to determine the tax consequences of the merger to you.

Laurel Hill Advisory Group

2 Robbins Lane, Suite 201

Jericho, New York 11753

Banks and Brokers: call (516) 933-3100

All Others: call toll free (888) 742-1305

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RISK FACTORS

In deciding how to vote, you should consider carefully all of the information included in this document and its annexes, all of the information incorporated by reference into the document and the risk factors identified by First Interstate with respect to First Interstate’s operations included in its filings with the SEC, including First Interstate’s Annual Report on Form 10-K for the year ended December 31, 2017. See “Where You Can Find More Information.” In addition, you should consider the following risk factors.

Risks Related to the Merger

Because the price of First Interstate Class A common stock will fluctuate, Northwest shareholders cannot be certain of the market value of the merger consideration.

Upon the completion of the merger, each share of Northwest common stock outstanding immediately before the completion of the merger will be converted into the right to receive 0.516 shares of First Interstate Class A common stock. The market value of the merger consideration may vary from the closing price of First Interstate Class A common stock on the date the execution of the merger agreement was announced, on the date that this document was mailed to Northwest shareholders, on the date of the Northwest special meeting and on the date the merger is completed. The market price of First Interstate Class A common stock may fluctuate as a result of a variety of factors, including general market and economic conditions, changes in First Interstate’s business, operations and prospects, and regulatory considerations. Therefore, at the time of the Northwest special meeting, Northwest shareholders will not know or be able to calculate the market value of the First Interstate Class A common stock they will receive upon completion of the merger. For example, based on the range of closing prices of First Interstate Class A common stock during the period from April 25, 2018, the last trading day before public announcement of the merger, through June 27, 2018, the last practicable date before the date of this document, the merger consideration represented a market value ranging from a low of $20.90 to a high of $23.09 for each share of Northwest common stock. You should obtain current market quotations for shares of First Interstate Class A common stock and Northwest common stock. See “Market Price and Dividend Information” on page 90 for ranges of historic market prices of First Interstate Class A common stock and Northwest common stock.

The price of First Interstate Class A common stock might decrease after the merger.

Upon completion of the merger, holders of Northwest common stock will become shareholders of First Interstate. First Interstate Class A common stock could decline in value after the merger. For example, during the twelve-month period ending on June 27, 2018 (the most recent practicable date before the printing of this document), the closing price of First Interstate Class A common stock varied from a low of $33.65 to a high of $44.75 and ended that period at $42.40. The market value of First Interstate Class A common stock fluctuates based upon general market conditions, First Interstate’s business, operations and prospects and other factors. Further, the market price of First Interstate Class A common stock after the merger may be affected by factors different from those currently affecting the common stock of First Interstate or Northwest. The businesses of Northwest and First Interstate differ and, accordingly, the results of operations of the combined company and the market price of the combined company’s shares of common stock may be affected by factors different from those currently affecting the independent results of operations and market prices of common stock of each of Northwest and First Interstate. For a discussion of the business of First Interstate and of certain factors to consider in connection with its business, see the documents incorporated by reference in this document and referred to under “Where You Can Find More Information” beginning on page 93.

Northwest and First Interstate will be subject to business uncertainties and contractual restrictions while the merger is pending.

Uncertainty about the effects of the merger on employees and customers may have an adverse effect on Northwest or First Interstate. These uncertainties may impair Northwest’s or First Interstate’s ability to attract,

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retain and motivate key personnel until the merger is completed, and could cause customers and others that interact with Northwest or First Interstate to seek to change existing business relationships with Northwest or First Interstate. Retention of certain employees by Northwest or First Interstate may be challenging while the merger is pending, as certain employees may experience uncertainty about their future roles with the combined company. If key employees depart because of issues relating to the uncertainty and difficulty of integration, or a desire not to remain with Northwest or First Interstate, Northwest’s business or First Interstate’s business could be harmed. In addition, subject to certain exceptions, Northwest has agreed to operate its business in the ordinary course before closing, which may prevent it from pursuing certain growth opportunities. See “Description of the Merger—Conduct of Business Before the Merger” for a description of the restrictive covenants applicable to Northwest and First Interstate.

Failure to complete the merger could negatively impact the stock prices and future businesses and financial results of First Interstate and Northwest.

There can be no assurance that the merger will be completed. If the merger is not completed, the ongoing businesses of First Interstate and Northwest may be adversely affected and First Interstate and Northwest will be subject to a number of risks, including the following:

In addition, if the merger is not completed, First Interstate and/or Northwest may experience negative reactions from the financial markets and from their respective customers and employees. First Interstate and/or Northwest also could be subject to litigation related to any failure to complete the merger or to proceedings commenced by First Interstate or Northwest against the other seeking damages or to compel the other to perform its obligations under the merger agreement. These factors and similar risks could have an adverse effect on the results of operation, business and stock prices of First Interstate and Northwest.

First Interstate may be unable to successfully integrate Northwest’s operations or retain Northwest’s employees, which could adversely affect the combined company.

The merger involves the integration of two companies that have previously operated independently. The difficulties of combining the operations of the two companies include, among other things: integrating personnel with diverse business backgrounds; combining different corporate cultures; and retaining key employees.

The process of integrating operations could cause an interruption of, or loss of momentum in, the activities of the business and the loss of key personnel. The integration of the two companies will substantially benefit from the experience and expertise of certain key employees of Northwest who are expected to be retained by First Interstate. First Interstate may not be successful in retaining these employees for the time period necessary to successfully integrate Northwest’s operations with those of First Interstate. The diversion of management’s attention and any delays or difficulties encountered in connection with the merger and the integration of the two companies’ operations could have an adverse effect on the business and results of operations of First Interstate following the merger.

Additionally, First Interstate may not be able to successfully achieve the level of cost savings, revenue enhancements and other synergies that it expects, and may not be able to capitalize upon the existing customer

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relationships of Northwest to the extent anticipated, or it may take longer, or be more difficult or expensive than expected, to achieve these goals. These matters could have an adverse effect on First Interstate’s business, results of operation and stock price.

The termination fee and the restrictions on solicitation contained in the merger agreement may discourage other companies from trying to acquire Northwest.

Until the completion of the merger, with some exceptions, Northwest is prohibited from soliciting, initiating, encouraging or participating in any discussion of or otherwise considering any inquiry or proposal that may lead to an acquisition proposal, such as a merger or other business combination transactions, with any person other than First Interstate. In addition, Northwest has agreed to pay a $5.1 million termination fee to First Interstate in specified circumstances. These provisions could discourage other companies that may have an interest in acquiring Northwest from considering or proposing such an acquisition even though those other companies might be willing to offer greater value to Northwest’s shareholders than First Interstate has offered in the merger. The payment of the termination fee would also have a material adverse effect on Northwest’s financial condition and results of operations.

Certain of Northwest’s directors and officers have interests that are different from, or in addition to, interests of Northwest shareholders generally.

Certain directors and officers of Northwest have interests in the merger that are different from, or in addition to, the interests of Northwest shareholders generally. These include: (1) employment and change in control agreements for certain directors and officers of Northwest and Inland Northwest Bank that provide for cash severance payments upon a termination without cause or a termination generally with good reason following the completion of the merger; (2) the acceleration of vesting of all outstanding restricted stock awards; (3) settlement agreements entered into with each of Russell A. Lee, President and Chief Executive Officer of Northwest, and Holly A. Poquette, Executive Vice President and Chief Financial Officer of Northwest, concurrent with the execution of the merger agreement; (4) a non-competition agreement and a consulting and release agreement entered into with Mr. Lee concurrent with the execution of the merger agreement; (5) continued employment of Mr. Lee as First Interstate Bank’s Executive Vice President of Special Projects; (6) continued employment of Ms. Poquette for up to six months to facilitate the integration of Inland Northwest Bank with First Interstate Bank; and (7) provisions in the merger agreement relating to indemnification of directors and officers and insurance for directors and officers of Northwest for events occurring before the merger. For a more detailed discussion of these interests, see “Description of the Merger—Interests of Certain Persons in the Merger that are Different from Yours” beginning on page 59.

Northwest shareholders will have a reduced ownership and voting interest after the merger and will exercise less influence over management of the combined organization.

First Interstate shareholders and Northwest shareholders each currently have the right to vote in the election of their respective board of directors and on various other matters affecting their respective company. Upon the completion of the merger, Northwest’s shareholders will become shareholders of First Interstate with a percentage ownership of the combined organization that is substantially smaller than such shareholders’ percentage ownership of Northwest.

The reduced voting power of Northwest shareholders is further effected by the two classes of common stock that First Interstate maintains. First Interstate Class B common stock is entitled to five votes per share, while shares of First Interstate Class A common stock, which is what will be issued to Northwest shareholders, are entitled to one vote per share. As of June 27, 2018, members of the Scott family held 362,124 shares of First Interstate Class A common stock and 21,721,123 shares of First Interstate Class B common stock and, therefore, controlled in excess of 72.9% of the voting power of First Interstate’s outstanding common stock. As a result, the Scott family will be able to exert a significant degree of influence or actual control over First Interstate’s

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management and affairs and over matters requiring shareholder approval, including the election of directors, a merger, consolidation or sale of all or substantially all of First Interstate’s assets and any other significant transaction. This concentrated control will limit Northwest shareholders’ future ability to influence corporate matters, and the interests of the Scott family may not always coincide with First Interstate’s interests or your interests.

The fairness opinion to the board of directors Northwest rendered on the date of the signing of the merger agreement does not reflect any changes in circumstances after the date of such fairness opinions.

D.A. Davidson delivered to the board of directors of Northwest its opinion on April 25, 2018. The opinion does not reflect changes that may occur or may have occurred after the date of such opinion, including changes to the operations and prospects of First Interstate or Northwest, changes in general market and economic conditions or regulatory or other factors that may materially alter or affect the value of First Interstate Class A common stock or Northwest common stock. The opinion speaks only as of the date on which it was rendered and not as of the date of this document or any other date.

There is no assurance when or even if the merger will be completed.

Completion of the merger is subject to satisfaction or waiver of a number of conditions. See “Description of the Merger—Conditions to Completing the Merger” beginning on page 63. There can be no assurance that First Interstate and Northwest will be able to satisfy the closing conditions or that closing conditions beyond their control will be satisfied or waived.

First Interstate and Northwest can agree at any time to terminate the merger agreement, even if Northwest shareholders have already voted to approve the merger agreement. First Interstate and Northwest can also terminate the merger agreement under other specified circumstances.

Regulatory approvals may not be received, may take longer than expected, or may impose conditions that are not presently anticipated or that could have an adverse effect on the combined company following the merger.

Before the merger and the bank merger may be completed, First Interstate and Northwest must obtain approvals from the Federal Reserve Board, the Montana Division and the Washington Department. Other approvals, waivers or consents from regulators may also be required. In determining whether to grant these approvals the regulators consider a variety of factors, including the regulatory standing of each party. An adverse development in either party’s regulatory standing or other factors could result in an inability to obtain approval or delay their receipt. These regulators may impose conditions on the completion of the merger or the bank merger or require changes to the terms of the merger or the bank merger. Such conditions or changes could have the effect of delaying or preventing completion of the merger or the bank merger or imposing additional costs on or limiting the revenues of the combined company following the merger and the bank merger, any of which might have an adverse effect on the combined company following the merger.

The shares of First Interstate Class A common stock to be received by Northwest shareholders as a result of the merger will have different rights from the shares of Northwest common stock.

Upon completion of the merger, Northwest shareholders will become First Interstate shareholders. Their rights as shareholders Class A common stock will be governed by Montana corporate law and the amended and restated articles of incorporation and bylaws of First Interstate. The rights associated with Northwest common stock are governed by Washington law and the articles of incorporation and bylaws of Northwest and are different from the rights associated with First Interstate Class A common stock. See the section of this document entitled “Comparison of Rights of Shareholders” beginning on page 81 for a discussion of the different rights associated with First Interstate Class A common stock.

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Goodwill incurred in the merger may negatively affect First Interstate’s financial condition.

To the extent that the merger consideration, consisting of shares of First Interstate Class A common stock to be issued in the merger, exceeds the fair value of the net assets, including identifiable intangibles of Northwest, that amount will be reported as goodwill by First Interstate. In accordance with current accounting guidance, goodwill will not be amortized but will be evaluated for impairment annually. A failure to realize expected benefits of the merger could adversely impact the carrying value of the goodwill recognized in the merger, and in turn negatively affect First Interstate’s financial condition.

Risks Relating to First Interstate’s Business

You should read and consider risk factors specific to First Interstate’s business that will also affect the combined company after the merger. These risks are described in the sections entitled “Risk Factors” in First Interstate’s Annual Report on Form 10-K for the fiscal year ended December 31, 2017 and in other documents incorporated by reference into this document. Please see the section entitled “Where You Can Find More Information” beginning on page 93 of this document for the location of information incorporated by reference into this document.

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CAUTIONARY STATEMENT ABOUT FORWARD-LOOKING STATEMENTS

Some of the statements contained or incorporated by reference in this document are forward looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 giving First Interstate’s or Northwest’s expectations or predictions of future financial or business performance or conditions. Forward-looking statements are typically identified by words such as “believe,” “expect,” “anticipate,” “intend,” “target,” “estimate,” “continue,” “projections,” “prospects” or “potential,” by future conditional verbs such as “will,” “would,” “should,” “could” or “may,” or by variations of such words or by similar expressions. Such forward-looking statements include, but are not limited to, statements about the benefits of the merger or the bank merger, including future financial and operating results of First Interstate, Northwest or the combined company following the merger, the combined company’s plans, objectives, expectations and intentions, cost savings and/or revenue enhancements to be achieved in the merger, the expected timing of the completion of the merger, financing plans and the availability of capital, the likelihood of success and impact of litigation and other statements that are not historical facts. These statements are only predictions based on First Interstate’s and Northwest’s current expectations and projections about future events. There are important factors that could cause First Interstate’s and Northwest’s actual results, level of activity, performance or achievements to differ materially from the results, level of activity, performance or achievements expressed or implied by the forward-looking statements. In particular, you should consider the numerous risks and uncertainties described in the section entitled “Risk Factors” beginning on page 14.

These forward-looking statements are subject to numerous assumptions, risks, and uncertainties that change over time. In addition to factors previously disclosed in First Interstate’s reports filed with the SEC, the following factors, among others, could cause actual results to differ materially from forward-looking statements:

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Additionally, the timing and occurrence or non-occurrence of events may be subject to circumstances beyond First Interstate’s or Northwest’s control.

Annualized, projected and estimated numbers are used for illustrative purposes only, are not forecasts and may not reflect actual results.

For any forward-looking statements made in this document or in any documents incorporated by reference into this document, First Interstate and Northwest claim the protection of the safe harbor for forward-looking statements contained in the Private Securities Litigation Reform Act of 1995. You are cautioned not to place undue reliance on these statements, which speak only as of the date of this document or the date of the applicable document incorporated by reference in this document. Except to the extent required by applicable law, neither First Interstate nor Northwest undertake to update forward-looking statements to reflect facts, circumstances, assumptions, or events that occur after the date the forward-looking statements are made. All written and oral forward-looking statements concerning the merger or other matters addressed in this document and attributable to First Interstate, Northwest, or any person acting on their behalf are expressly qualified in their entirety by the cautionary statements contained or referred to in this document.

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SELECTED HISTORICAL FINANCIAL AND OTHER DATA

The following tables present selected historical financial information for First Interstate and for Northwest at and for the dates indicated. The following information is only a summary and not necessarily indicative of the results of future operations of First Interstate, Northwest or the combined company. This information has been derived in part from and should be read in conjunction with the audited consolidated financial statements of First Interstate, which are incorporated by reference into this document. The financial information for First Interstate at December 31, 2017 and 2016 and for the three years ended December 31, 2017 should be read in connection with the audited consolidated financial statements and related notes thereto included in its Annual Report on Form 10-K for the year ended December 31, 2017. The financial information for First Interstate for the three months ended March 31, 2018 and 2017 should be read in connection with the unaudited financial statements and notes thereto included in its Quarterly Report on Form 10-Q for the three months ended March 31, 2018. The results of operations for the three months ended March 31, 2018 are not necessarily indicative of the operating results for the year ending December 31, 2018 or for any other period. See “Where You Can Find More Information” on page  93.

Selected Consolidated Historical Financial Data of First Interstate

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Selected Consolidated Historical Financial Data of Northwest

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UNAUDITED COMPARATIVE PRO FORMA PER SHARE DATA

The following table shows information about First Interstate’s and Northwest’s earnings per common share, dividends per share and book value per share, and similar information giving effect to the merger (which we refer to as “pro forma” information). In presenting the unaudited comparative pro forma information as of and for the periods shown, we assumed that First Interstate and Northwest had been merged on the date indicated or at the beginning of the periods presented, as applicable.

The information listed as “pro forma combined” was prepared using the exchange ratio of 0.516. The information listed as “per equivalent Northwest share” was obtained by multiplying the pro forma amounts by the exchange ratio of 0.516. First Interstate anticipates that the combined company will derive financial benefits from the merger that include reduced operating expenses and the opportunity to earn more revenue. The unaudited pro forma combined information, while helpful in illustrating the financial characteristics of First Interstate following the merger under one set of assumptions, does not reflect these benefits and, accordingly, does not attempt to predict or suggest future results. The unaudited pro forma combined information also does not necessarily reflect what the historical results of First Interstate would have been had our companies been combined during this period.

The information in the following table is based on, and should be read together with, the historical financial information that we have presented in or incorporated by reference in this document.

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SPECIAL MEETING OF NORTHWEST SHAREHOLDERS

This document is being provided to holders of Northwest common stock as Northwest’s proxy statement in connection with the solicitation of proxies by and on behalf of its board of directors to be voted at the Northwest special meeting and at any adjournment or postponement of the Northwest special meeting. This document is also being provided to holders of Northwest common stock as First Interstate’s prospectus in connection with the issuance by First Interstate of its shares of Class A common stock as consideration in the proposed merger.

Date, Time and Place of Meeting

The Northwest special meeting is scheduled to be held as follows:

Date: August 14, 2018

Time: 5:00 p.m., local time

Place: Airway Heights Branch of Inland Northwest Bank located at 11917 West Sunset Highway, Airway Heights, Washington

Purpose of the Meeting

At the Northwest special meeting, Northwest’s shareholders will be asked to:

Who Can Vote at the Meeting

You are entitled to vote if the records of Northwest showed that you held shares of Northwest common stock as of the close of business on June 27, 2018, which is the record date for the Northwest special meeting. As of the close of business on the record date, 7,267,205 shares of Northwest common stock were outstanding. Each share of Northwest common stock has one vote on each matter presented to shareholders. If your shares are held in “street name” by your broker, bank or other nominee and you wish to vote in person at the Northwest special meeting, you will have to obtain a “legal proxy” from your broker, bank or other nominee entitling you to vote at the Northwest special meeting.

Quorum; Vote Required

The Northwest special meeting will conduct business only if a majority of the outstanding shares of Northwest common stock is represented in person or by proxy at the meeting to constitute a quorum. If you submit valid proxy instructions or attend the meeting in person, your shares will be counted to determine whether there is a quorum, even if you abstain from voting. If you fail to provide voting instructions to your broker, bank or other nominee with respect to a proposal, that broker, bank or other nominee will not vote your shares with respect to that proposal.

Approval of the merger agreement requires the affirmative vote of two-thirds of the outstanding shares of Northwest common stock. Failure to submit valid proxy instructions or to vote in person will have the same effect as a vote against the merger agreement. Broker non-votes and abstentions from voting will have the same effect as voting against the merger agreement.

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Approval of the Northwest adjournment proposal requires that the votes cast in favor of the proposal exceed the votes cast against the proposal. The failure to vote in person or submit valid proxy instructions, broker non-votes and abstentions will have no effect on the voting on the proposal.

Shares Held by Northwest Officers and Directors and by First Interstate

As of June 27, 2018, directors and executive officers of Northwest beneficially owned 2,159,387 shares of Northwest common stock. This equals 28.8% of the outstanding shares of Northwest common stock as of June 27, 2018. Each of the directors and certain executive officers of Northwest, solely in their individual capacity as a Northwest shareholder, have entered into a separate voting agreement with First Interstate to vote the 1,937,220 shares of Northwest common stock eligible to be voted at the special meeting by them in favor of the merger agreement. As of June 27, 2018, neither First Interstate nor any of its subsidiaries, directors or executive officers owned any shares of Northwest common stock.

Voting and Revocability of Proxies

You may vote in person at the Northwest special meeting or by proxy. To ensure your representation at the Northwest special meeting, Northwest recommends that you vote by proxy even if you plan to attend the Northwest special meeting. You can change your vote at the special meeting.

If you are a “shareholder of record,” you can vote your shares:

Please refer to the specific instructions set forth on the proxy card. We encourage you to vote via the internet or by telephone.

Northwest shareholders whose shares are held in “street name” by their broker, bank or other nominee must follow the instructions provided by their broker, bank or other nominee to vote their shares. Your broker, bank or other nominee may allow you to deliver your voting instructions via telephone or the internet. If your shares are held in “street name” and you wish to vote in person at the Northwest special meeting, you will have to obtain a “legal proxy” from your broker, bank or other nominee entitling you to vote at the special meeting.

If you are a holder of record of Northwest common stock, voting instructions are included on the enclosed proxy card. If you properly complete and timely submit your proxy, your shares will be voted as you have directed. You may vote for, against or abstain with respect to each matter. If you are the holder of record of your shares of Northwest common stock and submit your proxy without specifying a voting instruction, your shares of Northwest common stock will be voted “FOR” the proposal to approve the merger agreement and “FOR” the Northwest adjournment proposal. If your shares are held in street name and you return an incomplete instruction card to your broker, bank or other nominee, that broker, bank or other nominee will not vote your shares with respect to any matter.

You may revoke your proxy at any time before it is voted at the special meeting by:

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If your shares are held in “street name,” you should contact your broker, bank or other nominee to change your vote.

Attendance at the Northwest special meeting will not, in and of itself, constitute a revocation of a proxy. All written notices of revocation and other communication with respect to the revocation of proxies should be addressed to:

Northwest Bancorporation, Inc.

421 West Riverside Avenue, Suite 113

Spokane, Washington 99201

Attention: Leilani T. McKernan, Corporate Secretary

Solicitation of Proxies

Northwest will pay for the solicitation of proxies from Northwest shareholders. In addition to soliciting proxies by mail, Laurel Hill Advisory Group, a proxy solicitation firm, will assist Northwest in soliciting proxies for the Northwest special meeting. Northwest will pay $6,000 for these services plus out-of-pocket expenses. Additionally, directors, officers and employees of Northwest and Inland Northwest Bank may solicit proxies personally and by telephone. None of these persons will receive additional or special compensation for soliciting proxies. Northwest will, upon request, reimburse brokers, banks and other nominees for their expenses in sending proxy materials to their customers who are beneficial owners and obtaining their voting instructions.

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NORTHWEST PROPOSAL NO. 1

APPROVAL OF THE MERGER AGREEMENT

At the Northwest special meeting, shareholders will consider and vote on a proposal to approve the merger agreement. Details about the merger agreement, including each party’s reasons for the merger, the effect of approval of the merger agreement and the timing of effectiveness of the merger, are discussed in the section entitled “Description of the Merger” beginning on page 30 of this document.

Northwest’s board of directors unanimously recommends

that Northwest shareholders vote “FOR”

approval of the merger agreement.

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NORTHWEST PROPOSAL NO. 2

ADJOURNMENT OF THE NORTHWEST SPECIAL MEETING

If there are insufficient proxies at the time of the Northwest special meeting to approve the merger agreement, Northwest shareholders may be asked to vote on a proposal to adjourn the meeting to a later date to allow additional time to solicit additional proxies. Northwest’s board of directors does not currently intend to propose adjournment at the Northwest special meeting if there are sufficient votes to approve the merger agreement (Proposal No. 1).

Northwest’s board of directors unanimously recommends

that Northwest shareholders vote “FOR”

approval of the Northwest adjournment proposal.

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DESCRIPTION OF THE MERGER

The following summary of the merger agreement is qualified by reference to the complete text of the merger agreement. A copy of the merger agreement is attached as Annex A to this document and is incorporated by reference into this document. You should read the merger agreement completely and carefully as it, rather than this description, is the legal document that governs the merger.

General

The merger agreement provides for the merger of Northwest with and into First Interstate, with First Interstate as the surviving entity. Following the merger of Northwest with First Interstate, Inland Northwest Bank will merge with and into First Interstate Bank, with First Interstate Bank as the surviving entity.

Consideration to be Received in the Merger

When the merger becomes effective, each share of Northwest common stock issued and outstanding immediately before completion of the merger will automatically be converted into the right to receive 0.516 shares of First Interstate Class A common stock, plus cash in lieu of any fractional share, without interest.

If First Interstate declares a stock dividend or distribution on shares of its common stock or subdivides, splits, reclassifies or combines the shares of First Interstate Class A common stock before the effective time of the merger, then the exchange ratio will be adjusted to provide Northwest shareholders with the same economic effect as contemplated by the merger agreement before any of these events.

Northwest’s shareholders will not receive fractional shares of First Interstate Class A common stock. Instead, Northwest’s shareholders will receive a cash payment for any fractional shares in an amount equal to the product of (1) the fraction of a share of First Interstate Class A common stock to which he, she or it is entitled multiplied by (2) the average closing sales price of First Interstate Class A common stock over the 20 consecutive trading days ending on and including the fifth day before the closing date of the merger.

Background of the Merger

As part of ongoing consideration and evaluation of Northwest’s long-term prospects and strategies, Northwest’s board of directors and senior management have regularly reviewed and assessed business strategies and objectives, including strategic opportunities and challenges, and have considered various strategic options potentially available to Northwest, all with the goal of enhancing value for Northwest shareholders. The strategic discussions have focused on, among other things, remaining as a stand-alone company, the costs and benefits associated with becoming a public company, the business and regulatory environment facing financial institutions generally and Northwest, in particular, as well as conditions and ongoing consolidation in the financial services industry.

As part of this ongoing evaluation, the Northwest board of directors considered the merits of selling the institution, merging with another institution of similar size and complementary business, or remaining independent, as well as the challenges of remaining competitive in the current economic, regulatory and interest rate climate, and the potentially increased operating costs associated with regulatory compliance, technology investment and competitive forces.

On September 19, 2017, D.A. Davidson was invited to present various strategic alternatives with the Northwest board of directors, including the benefits and challenges of pursuing organic growth, an acquisition strategy, merger transactions, an initial public offering (which we refer to as an “IPO”), or outright strategic sale of Northwest, and to discuss the overall market conditions. Following this meeting, the Northwest board of directors decided to pursue the IPO strategy.

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On December 19, 2017, D.A. Davidson discussed with the Northwest board of directors the IPO market conditions, strategy for an IPO, potential timeline and D.A. Davidson’s experience in leading public offerings for bank holding companies.

On January 19, 2018, D.A. Davidson was retained by the Northwest board of directors to serve as lead managing underwriter for Northwest to conduct an IPO to raise capital for strategic growth opportunities and potentially to repay indebtedness. Subsequently, D.A. Davidson and Northwest began due diligence and preparing necessary offering documentation.

On February 20, 2018, Northwest’s CEO directed D.A. Davidson to contact prospective acquirers to determine if there was any interest in an acquisition of Northwest, as an alternative to and in comparison with Northwest’s IPO strategy. Northwest approved a list of four companies to be contacted to solicit potential interest for an acquisition of Northwest. Two of the prospective acquirers expressed interest, including First Interstate and another bank (which we refer to as “Bank B”) each of which signed a confidentiality agreement to receive confidential information about Northwest. The confidentiality agreements did not restrict Northwest from negotiating or entering into a definitive agreement with any other party at any time. D.A. Davidson requested for both First Interstate and Bank B to submit non-binding indication of interest by March 13, 2018, which would identify, among other items, the proposed purchase price, the form of consideration, the plans for the combined company, timeline to complete a transaction and conditions and approvals required to complete a strategic transaction.

In early March 2018, Russell A. Lee, the CEO of Northwest, had in-person meetings with the CEOs of both First Interstate and Bank B, respectively.

On March 9, 2018, First Interstate sent a non-binding indication of interest letter to Northwest which provided for 100% stock consideration based on a fixed exchange ratio of 0.5 shares of First Interstate common stock for each share of Northwest common stock. Based on market prices as of such date, the consideration was valued at $20.78 per share or aggregate merger consideration of $157.7 million.

On March 13, 2018, D.A. Davidson provided the Northwest board of directors a status update for the IPO project and discussed the pro forma impact of the IPO, including the dilution to be incurred based on a range of offer prices and size of the offering, and a market update, including valuation and performance metrics of Northwest’s publicly traded peers. Subsequently, D.A. Davidson provided an update to the Northwest board regarding the discussions with First Interstate and Bank B, including an overview of the non-binding indication of interest letter from First Interstate. D.A. Davidson explained Bank B was expected to submit a non-binding indication of interest letter during the next week. The Northwest board discussed the proposed terms of the non-binding indication of interest letter and the benefits to shareholders, employees and customers provided by the merger and the relative benefits of proceeding with the merger or continuing with the public offering, noting the execution risk associated with pursuing the public offering. The Northwest board then instructed Mr. Lee and D.A. Davidson to negotiate certain terms with First Interstate for a revised offer, and to continue discussions with Bank B.

On March 19, 2018, D.A. Davidson and Northwest executed an engagement agreement for D.A. Davidson to render financial advisory and investment banking services to Northwest. D.A. Davidson also agreed to provide the Northwest board of directors with a fairness opinion.

On March 23, 2018, representatives of Bank B and D.A. Davidson held a phone call, whereby Bank B verbally indicated a valuation range of $20.50 to $21.50 per share for Northwest. Bank B explained a written indication would be sent the following week.

On March 23, 2018 representatives of D.A. Davidson participated in a conference call to update the Northwest board of directors on the written indication received from First Interstate and the verbal proposal

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received from Bank B. Further discussions occurred between Northwest and First Interstate and between Northwest and Bank B.

On March 27, 2018, Bank B submitted its non-binding indication of interest letter to Northwest, which included a range of consideration of $20.09 per share to $21.00 per share, or aggregate consideration of $152.3 million to $159.3 million, based on market prices as of such date.

On March 27, 2018, First Interstate sent a revised indication of interest letter to Northwest for an exchange ratio of 0.516, an increase of 3.2% compared to the original written indication dated March 9, 2018. Based on market prices as of such date, the consideration was valued at $20.15 per share, or aggregate of $152.9 million.

On March 27, 2018, representatives of D.A. Davidson participated on a conference call with Northwest’s board of directors to further discuss the two indications from First Interstate and Bank B. D.A. Davidson discussed and compared the two non-binding indications of interest, including the proposed merger consideration and other terms described in the two proposals, and compared each company’s financial performance, stock price trading history and dividend history, among other things. In particular, the Northwest board of directors discussed the upside to Northwest shareholders, relative to the proposal received from Bank B, of potential dividend payments from First Interstate if First Interstate continued to issue dividend payments consistent with its dividend payment history. The Northwest board of directors also discussed the advantages of First Interstate’s existing market footprint being complementary to the Northwest existing market footprint, in contrast to Bank B, for whom the Pacific Northwest would be a new market. Following this discussion, the Northwest board of directors voted to authorize Mr. Lee to execute the non-binding indication of interest with First Interstate, and concurrently enter into a period of exclusivity with First Interstate for 35 days. Subsequent to executing the non-binding indication of interest, both First Interstate and Northwest organized remaining due diligence to be completed and coordinated for in-person management meetings.

On March 29, 2018, Northwest received a draft version of the definitive merger agreement from First Interstate, and the parties began negotiating the terms of the merger agreement with respective legal and financial advisors.

On March 29, 2018, Northwest and D.A. Davidson sent a reverse due diligence request list to First Interstate and its advisors. Subsequently, First Interstate began uploading information into an online data room, and the parties conducted a conference call on April 10, 2018 with First Interstate’s CEO and CFO.

On April 17, 2018, Northwest’s board of directors held a meeting with Witherspoon Kelley, its legal counsel, and D.A. Davidson to review the current draft of the merger agreement. D.A. Davidson provided an overview of the financial aspects of the proposed transaction, including the value of the merger consideration based on updated prices, and, among other things, comparative information relative to similar merger transactions. Further, Witherspoon Kelley reviewed the draft merger agreement and addressed questions from the board members. Following the meeting, the board of directors instructed Northwest management, Witherspoon Kelley and D.A. Davidson to complete the remaining open items in the merger agreement and ancillary agreements.

On April 23, 2018, First Interstate’s board of directors held a meeting at which representatives of First Interstate’s senior management were present and representatives from its financial advisor, Sandler O’Neill & Partners, L.P. (which we refer to as “Sandler”), and its legal counsel, Luse Gorman, PC (which we refer to as “Luse Gorman”), were present via telephone. Representatives of Sandler reviewed the financial aspects of the transaction and the financial analysis supporting its opinion. After discussion among First Interstate’s board of directors and its advisors, representatives of Sandler delivered its opinion, dated April 23, 2018, to First Interstate’s board of directors to the effect that, as of such date and based on and subject to the qualifications, limitations and assumptions stated in its opinion, the exchange ratio to be paid to the Northwest shareholders by First Interstate in the proposed merger was fair to First Interstate from a financial point of view. First Interstate’s

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board of directors was updated on the results of the completion of the legal and business due diligence review of Northwest. A representative of Luse Gorman reviewed in detail the terms of the merger agreement. After further discussion, First Interstate’s board of directors unanimously approved the merger agreement.

On April 23, 2018, Northwest’s board of directors held a meeting at which Mr. Lee advised the Northwest board of directors that First Interstate’s board of directors had approved the merger agreement. Mr. Lee also updated the Northwest board of directors regarding the impact the proposed transaction was expected to have on certain employees, noting that he and Chad Burchard were both expected to be retained by First Interstate following consummation of the merger to help ensure key Northwest personnel would be retained by First Interstate following the merger. The Northwest board of directors further discussed the impact of the proposed transaction on Northwest’s shareholders, employees, customers and the communities it serves.

On April 25, 2018, Northwest held a board of directors meeting at which the board of directors reviewed the final form of the merger agreement and ancillary agreements. Further, D.A. Davidson presented its opinion to the board of directors at this meeting, to the effect that, as of such date and subject to the procedures followed, assumptions made, matters considered and qualifications and limitations on the review undertaken by D.A. Davidson as set forth in such opinion, that the exchange ratio to be paid to the Northwest shareholders in the transaction was fair from a financial point of view. Following discussion of the relative benefits of the proposed transaction with First Interstate to Northwest shareholders, employees and customers, the board of directors voted to approve the merger agreement. Later that day, First Interstate and Northwest entered into the merger agreement and issued a joint press release announcing the transaction. The parties to the voting agreements also entered into the voting agreements.

Northwest’s Reasons for the Merger and Recommendation of the Board of Directors

The Northwest board of directors believes the merger is in the best interests of the Northwest shareholders. After careful consideration, the Northwest board of directors unanimously approved the merger agreement at a meeting held on April 25, 2018 and recommends that Northwest shareholders vote “FOR” approval of the merger agreement and “FOR” adjournment of the meeting to a later date or dates to permit further solicitation of proxies, if necessary.

In reaching its determination to unanimously approve the merger agreement, the Northwest board of directors consulted with Northwest’s management, D.A. Davidson and Witherspoon Kelley and considered a number of factors. Following is a description of each of the material factors that the Northwest board of directors believes favor the merger:

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In the course of its deliberations regarding the merger, the Northwest board of directors also considered the following information that the Northwest board of directors determined did not outweigh the benefits to Northwest and its shareholders expected to be generated by the merger:

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The above discussion of the information and factors considered by the Northwest board of directors is not intended to be exhaustive, but includes the material factors the board of directors considered. In reaching its determination to approve and recommend the acquisition, the board of directors did not assign any relative or specific weights to the foregoing factors, and individual directors may have given differing weights to different factors. The Northwest board of directors also did not undertake to make any specific determination as to whether any factor was decisive in reaching its ultimate determination. The Northwest board of directors instead based its recommendation on the totality of the information presented.

In considering the recommendation of the Northwest board of directors with respect to the proposal to adopt and approve the merger agreement, Northwest shareholders should be aware that Northwest’s directors and executive officers have interests in the merger that may be different from, or in addition to, those of other Northwest shareholders. The board of directors was aware of and considered these interests, among other matters, in evaluating and negotiating the merger agreement and the merger and in recommending that the merger agreement be approved by Northwest’s shareholders. See “—Interests of Certain Persons in the Merger that are Different from Yours.”

In the course of its deliberations with respect to the merger, the Northwest board of directors discussed the anticipated impact of the merger on Northwest, its shareholders, and its various other constituencies, and determined that the benefits to Northwest and its constituencies expected to result from the merger would likely outweigh any disadvantages identified during the board of directors’ deliberations.

For the reasons set forth above, the Northwest board of directors determined that the merger, the merger agreement and the transactions contemplated by the merger agreement are advisable and in the best interests of Northwest’s shareholders, and approved the merger agreement. The Northwest board of directors unanimously recommends that the Northwest shareholders vote “FOR” the approval of the merger agreement and “FOR” the Northwest adjournment proposal.

This summary of the reasoning of the Northwest board of directors and other information presented in this section is forward-looking in nature and, therefore, should be read in light of the factors discussed under “Cautionary Statement About Forward-Looking Statements.”

D.A. Davidson’s Opinion to Northwest’s Board of Directors

On March 19, 2018, Northwest entered into an engagement agreement with D.A. Davidson to render financial advisory and investment banking services to Northwest. As part of its engagement, D.A. Davidson agreed to assist Northwest in analyzing, structuring, negotiating and, if appropriate, effecting a transaction between Northwest and another corporation or business entity. D.A. Davidson also agreed to provide

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Northwest’s board of directors with an opinion as to the fairness, from a financial point of view, of the exchange ratio to the holders of Northwest’s common stock in the proposed merger. Northwest engaged D.A. Davidson because D.A. Davidson is a nationally recognized investment banking firm with substantial experience in transactions similar to the merger and is familiar with Northwest and its business. As part of its investment banking business, D.A. Davidson is continually engaged in the valuation of financial institutions and their securities in connection with mergers and acquisitions and other corporate transactions.

On April 25, 2018, the Northwest board of directors held a meeting to evaluate the proposed merger. At this meeting, D.A. Davidson reviewed the financial aspects of the proposed merger and rendered an opinion to the Northwest board that, as of such date and based upon and subject to assumptions made, procedures followed, matters considered and limitations on the review undertaken, the exchange ratio was fair, from a financial point of view, to holders of Northwest’s common stock in the proposed merger.

The full text of D.A. Davidson’s written opinion, dated April 25, 2018, is attached as Annex C to this document and is incorporated herein by reference. The description of the opinion set forth herein is qualified in its entirety by reference to the full text of such opinion. Northwest’s shareholders are urged to read the opinion in its entirety.

D.A. Davidson’s opinion speaks only as of the date of the opinion and D.A. Davidson undertakes no obligation to revise or update its opinion. The opinion is directed to the Northwest board of directors and addresses only the fairness, from a financial point of view, of the exchange ratio to the holders of Northwest’s common stock in the proposed merger. The opinion does not address, and D.A. Davidson expresses no view or opinion with respect to, (1) the underlying business decision of Northwest to engage in the merger, (2) the relative merits or effect of the merger as compared to any alternative business transactions or strategies that may be or may have been available to or contemplated by Northwest or Northwest’s board of directors, or (3) any legal, regulatory, accounting, tax or similar matters relating to Northwest, its shareholders or relating to or arising out of the merger. The opinion expresses no view or opinion as to any terms or other aspects of the merger, except for the merger consideration. Northwest and First Interstate determined the exchange ratio through the negotiation process. The opinion does not constitute a recommendation to any Northwest shareholder as to how such shareholder should vote at the Northwest meeting on the merger or any related matter. The opinion does not express any view as to the amount or nature of the compensation to any of Northwest’s officers, directors or employees, or any class of such persons, relative to the merger consideration, or with respect to the fairness of any such compensation. The opinion has been reviewed and approved by D.A. Davidson’s Fairness Opinion Committee in conformity with its policies and procedures established under the requirements of Rule 5150 of the Financial Industry Regulatory Authority.

D.A. Davidson has reviewed the Registration Statement on Form S-4 of which this document is a part and consented to the inclusion of its opinion to the Northwest board of directors as Annex C to this document and to the references to D.A. Davidson and its opinion contained herein. A copy of the consent of D.A. Davidson is attached as Exhibit 99.2 to the Registration Statement on Form S-4.

In connection with rendering its opinion, D.A. Davidson reviewed, among other things, the following:

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In arriving at its opinion, D.A. Davidson assumed and relied upon the accuracy and completeness of all information supplied or otherwise made available to D.A. Davidson, discussed with or reviewed by or for D.A. Davidson, or publicly available, and D.A. Davidson did not independently verify, and did not assume responsibility for independently verifying, such information or undertake an independent evaluation or appraisal of any of the assets or liabilities (contingent or otherwise) of Northwest or First Interstate, nor did D.A. Davidson make an independent appraisal or analysis of Northwest or First Interstate with respect to the merger. In addition, D.A. Davidson did not assume any obligation to conduct, nor did D.A. Davidson conduct, any physical inspection of the properties or facilities of Northwest or First Interstate and has not been provided with any reports of such physical inspections. D.A. Davidson did not make an independent evaluation or appraisal of the adequacy of the allowance for loan losses of Northwest or First Interstate nor has D.A. Davidson reviewed any individual credit files relating to Northwest or First Interstate. D.A. Davidson assumed that the respective allowances for loan losses for both Northwest and First Interstate are adequate to cover such losses and will be adequate on a pro forma basis for the combined entity. D.A. Davidson assumed that there has been no material change in Northwest’s or First Interstate’s assets, financial condition, results of operations, cash flows, business or prospects since the date of the most recent financial statements provided to D.A. Davidson and that neither Northwest and First Interstate is party to any material pending transaction, including without limitation any financing, recapitalization, acquisition or merger, divestiture or spin-off, other than the merger. D.A. Davidson assumed in all respects material to its analysis that Northwest and First Interstate will remain as going concerns for all periods relevant to its analysis. D.A. Davidson also assumed in all respects material to its analysis that all of the representations and warranties contained in the merger agreement and all related agreements are true and correct. D.A. Davidson has assumed that in the course of obtaining the necessary regulatory or other consents or approvals (contractual or otherwise) for the merger, no restrictions, including any divestiture requirements or amendment or modifications, will be imposed that will have a material adverse effect on Northwest or the contemplated benefits of the merger. D.A. Davidson’s opinion was necessarily based upon information available to D.A. Davidson and economic, market, financial and other conditions as they exist and can be evaluated on the date the fairness opinion letter was delivered to Northwest’s board of directors.

With respect to the financial forecasts and other analyses (including information relating to certain pro forma financial effects of, and strategic implications and operational benefits anticipated to result from, the transaction) provided to or otherwise reviewed by or for or discussed with D.A. Davidson, D.A. Davidson was

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advised by management of Northwest that such forecasts and other analyses were reasonably prepared on bases reflecting the best currently available estimates and good faith judgments of management of Northwest as to the future financial performance of Northwest and the other matters covered thereby, and that the financial results (including the potential strategic implications and operational benefits anticipated to result from the transaction) reflected in such forecasts and analyses will be realized in the amounts and at the times projected. D.A. Davidson assumes no responsibility for and expresses no opinion as to these forecasts and analyses or the assumptions on which they were based. D.A. Davidson has relied on the assurances of management of Northwest that they are not aware of any facts or circumstances that would make any of such information, forecasts or analyses inaccurate or misleading.

D.A. Davidson did not make an independent evaluation of the quality of Northwest’s or First Interstate’s deposit base, nor has D.A. Davidson independently evaluated potential deposit concentrations or the deposit composition of Northwest or First Interstate. D.A. Davidson did not make an independent evaluation of the quality of Northwest’s or First Interstate’s investment securities portfolio, nor has D.A. Davidson independently evaluated potential concentrations in the investment securities portfolio of Northwest or First Interstate.

D.A. Davidson’s opinion does not take into account individual circumstances of specific holders with respect to control, voting or other rights which may distinguish such holders.

D.A. Davidson does not express any opinion as to the value of any asset of Northwest whether at current market prices or in the future, or as to the price at which Northwest or its assets could be sold in the future. D.A. Davidson also expresses no opinion as to the price at which Northwest’s common stock or First Interstate’s common stock will trade following announcement of the transaction or at any future time.

D.A. Davidson has not evaluated the solvency or fair value of Northwest or First Interstate under any state, federal or other laws relating to bankruptcy, insolvency or similar matters. This opinion is not a solvency opinion and does not in any way address the solvency or financial condition of Northwest or First Interstate. D.A. Davidson is not expressing any opinion as to the impact of the transaction on the solvency or viability of Northwest or First Interstate or the ability of Northwest or First Interstate to pay their respective obligations when they come due.

Set forth below is a summary of the material financial analyses performed by D.A. Davidson in connection with rendering its opinion. The summary of the analyses of D.A. Davidson set forth below is not a complete description of the analysis underlying its opinion, and the order in which these analyses are described below is not indicative of any relative weight or importance given to those analyses by D.A. Davidson. The following summaries of financial analyses include information presented in tabular format. You should read these tables together with the full text of the summary financial analyses, as the tables alone are not a complete description of the analyses.

Unless otherwise indicated, the following quantitative information, to the extent it is based on market data, is based on market data as of April 23, 2018 and is not necessarily indicative of market conditions after such date.

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Implied Valuation Multiples for Northwest based on the Merger Consideration

D.A. Davidson reviewed the financial terms of the proposed transaction. As described in the merger agreement, each outstanding share of common stock of Northwest will be converted into the right to receive 0.516 shares of First Interstate Class A common stock. The terms and conditions of the merger are more fully described in the merger agreement. For purposes of the financial analyses described below, based on the closing price of First Interstate Class A common stock on April 23, 2018 of $40.45, the exchange ratio represented an implied value of $20.87 per share of Northwest common stock. Based upon financial information as of or for the twelve-month period ended March 31, 2018 and other financial and market information described below, D.A. Davidson calculated the following transaction ratios:

Transaction Ratios

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Stock Price Performance of First Interstate and Northwest

D.A. Davidson reviewed the history of the reported trading prices and volume of Northwest common stock and First Interstate Class A common stock and the relationship between the movements in the prices of Northwest common stock and First Interstate Class A common stock to movements in certain stock indices, including the Russell 3000 and the KBW Regional Bank Index. D.A. Davidson also compared the stock price performance of Northwest or First Interstate with the performance of the Russell 3000 and the KBW Nasdaq Regional Banking Index as follows:

One Year Stock Performance

Three Year Stock Performance

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Contribution Analysis

D.A. Davidson analyzed the relative contribution of Northwest and First Interstate to certain financial and operating metrics for the pro forma combined company. Such financial and operating metrics included: (1) market capitalization; (2) adjusted net income during the preceding twelve months ended March 31, 2018; (3) estimates of First Interstate net income in 2018 and 2019 using U.S. generally accepted accounting principles (which we refer to as “GAAP”) and based on publicly available consensus street estimates and estimates of Northwest GAAP net income in 2018 and 2019 based on Northwest management’s budget; (4) total assets; (5) gross loans; (6) total deposits; (7) non-interest bearing demand deposits; (8) non-maturity deposits; and (9) tangible common equity. The relative contribution analysis did not give effect to the impact of any synergies as a result of the proposed merger. The results of this analysis are summarized in the table below, which also compares the results of this analysis with the implied pro forma ownership percentages of First Interstate or Northwest shareholders in the combined company based on the exchange ratio:

Contribution Analysis

Note: Pro forma contribution does not include any purchase accounting or merger adjustments

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Northwest Comparable Companies Analysis

D.A. Davidson used publicly available information to compare selected financial and market trading information for Northwest and a group of 12 financial institutions selected by D.A. Davidson which: (1) were headquartered in Washington, Oregon and Idaho; (2) had their common stock listed on an over-the-counter exchange; (3) had assets greater $300 million; and (4) were not pending merger targets or ethnic banks. The 12 financial institutions were as follows:

The analysis compared the financial condition and market performance of Northwest and the 12 financial institutions identified above based on publicly available financial and market trading information for Northwest and the 12 financial institutions as of and for the twelve-month or three-month period ended March 31, 2018. The table below shows the results of this analysis (excluding the impact of earnings per share multiples considered not meaningful by D.A. Davidson).

Financial Condition and Performance

Market Performance Multiples

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First Interstate Comparable Companies Analysis

D.A. Davidson used publicly available information to compare selected financial and market trading information for First Interstate and a group of 13 financial institutions selected by D.A. Davidson which: (1) were headquartered in the western portion of the United States; (2) had their common stock listed on the NASDAQ or New York Stock Exchange; (3) had assets between $5.0 billion and $25.0 billion; and (4) were not pending merger targets or ethnic banks. These 13 financial institutions were as follows:

The analysis compared the financial condition and market performance of First Interstate and the 13 financial institutions identified above based on publicly available financial and market trading information for First Interstate and the 13 financial institutions as of and for the twelve-month or three-month period ended March 31, 2018. The 2018 and 2019 earnings per share multiples for First Interstate and the 13 financial institutions identified above based on publicly available consensus street estimates for First Interstate and the 13 financial institutions. The table below shows the results of this analysis (excluding the impact of earnings per share multiples considered not meaningful by D.A. Davidson).

Financial Condition and Performance

Market Performance Multiples

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