First Financial to merge with First Illinois in 2026

FIRST FINANCIAL CORP (THFF) announced that First Illinois Corporation has entered into a merger agreement with First Financial, with Hickory Point Bank expected to merge into First Financial Bank, NA.

Rhea-AI Filing Summary

FIRST FINANCIAL CORP (THFF) announced that First Illinois Corporation has entered into a merger agreement with First Financial, with Hickory Point Bank expected to merge into First Financial Bank, NA. The transaction is targeted for completion in the fourth quarter of 2026.

First Financial plans to file a registration statement on Form S-4, which will include a proxy statement of First Illinois that also serves as a prospectus of First Financial and will be sent to First Illinois shareholders. The communication states it is not an offer or a solicitation, and emphasizes that shareholders should carefully read the proxy statement/prospectus and related SEC filings when available.

Key Figures

Expected merger completion period: Fourth quarter of 2026 Form S-4: Registration statement on Form S-4 2026 annual meeting proxy filing date: March 17, 2026

3 metrics

Expected merger completion period Fourth quarter of 2026 Targeted timing for completion of the merger of First Illinois with First Financial and Hickory Point Bank with First Financial Bank, NA

Form S-4 Registration statement on Form S-4 Filing to register securities and provide the proxy statement/prospectus to First Illinois shareholders

2026 annual meeting proxy filing date March 17, 2026 Date First Financial filed its definitive proxy statement for its 2026 annual meeting with the SEC

Key Terms

registration statement on Form S-4, proxy statement/prospectus, Participants in the Solicitation, Section 10 of the Securities Act of 1933

4 terms

registration statement on Form S-4 regulatory

"First Financial will file materials with the SEC, including a registration statement on Form S-4"

A registration statement on Form S-4 is a formal filing with the U.S. Securities and Exchange Commission used when a company issues shares or other securities as part of a merger, acquisition, exchange offer or similar corporate deal. It bundles the transaction terms, financial statements, risk factors and shareholder vote materials so investors can assess the deal; think of it as a detailed prospectus or buyer’s packet that explains what you would own and how the deal could change your stake.

proxy statement/prospectus regulatory

"The registration statement will include a proxy statement of First Illinois that also constitutes a prospectus"

A proxy statement or prospectus is a document that companies send to shareholders to provide important information about upcoming decisions or investments, such as voting on company issues or offering new shares to the public. It helps investors understand the details and risks involved, enabling them to make informed choices about their ownership or involvement with the company.

Participants in the Solicitation regulatory

"Participants in the Solicitation First Financial, First Illinois and their respective directors"

People or firms who actively seek to influence shareholders’ choices in a corporate action—such as a vote, merger, proxy contest, or tender offer. This can include company insiders, advisers, bankers, lawyers and professional solicitors who contact investors to persuade them. Investors care because knowing who is doing the persuading reveals potential conflicts, resources and credibility behind the campaign, much like checking who is organizing a political campaign before accepting its message.

Section 10 of the Securities Act of 1933 regulatory

"No offer of securities or solicitation will be made except by means of a prospectus meeting the requirements of Section 10"

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What merger involving THFF is described in this communication?

First Illinois Corporation has entered into a merger agreement with First Financial Corporation (THFF), under which Hickory Point Bank will merge with First Financial Bank, NA. This combination is presented as a partnership to provide greater scale and resources while maintaining community banking focus.

When is the First Financial (THFF) and First Illinois merger expected to close?

The merger between First Financial Corporation and First Illinois Corporation, with Hickory Point Bank merging into First Financial Bank, NA, is expected to be completed in the fourth quarter of 2026, subject to customary conditions and processes.

What SEC filing will First Financial (THFF) use for the merger with First Illinois?

First Financial will file a registration statement on Form S-4. This filing will include a proxy statement of First Illinois that also constitutes a prospectus of First Financial and will be sent to First Illinois’ shareholders in connection with the proposed merger.

How can First Illinois shareholders obtain merger documents for THFF’s transaction?

Shareholders can obtain the Form S-4, proxy statement/prospectus, and related documents free of charge from the SEC’s website at www.sec.gov or via First Financial’s investor relations website. They may also request copies in writing or by calling the number provided by First Financial.

Is this First Financial (THFF) communication an offer to sell securities or solicit votes?

No. The communication explicitly states it does not constitute an offer to sell or a solicitation of an offer to buy securities, nor a solicitation of any vote, in any jurisdiction. Any offer or solicitation will only be made by a prospectus meeting Section 10 of the Securities Act of 1933.

Who may be participants in the proxy solicitation for the THFF–First Illinois merger?

First Financial, First Illinois, and their respective directors and executive officers may be deemed participants in soliciting proxies from First Illinois’ shareholders. Information on these individuals and their interests will be set forth in the Form S-4 and related materials.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 09/10/2026 - 02:47 PM Accepted by SEC EDGAR 09/10/2026 - 02:43 PM Learn about SEC filing dates

Filed by First Financial Corporation

Pursuant to Rule 425 under the Securities Act of 1933

and deemed filed pursuant to Rule 14a-12

under the Securities Exchange Act of 1934

Subject Company: First Illinois Corporation

Commission File No.: 0-16759

Date: September 10, 2026

[DATE]

[CLIENT NAME]

[ADDRESS]

[CITY, ST ZIP]

Dear [CLIENT NAME],

Re: Important Update from Hickory Point Bank

For generations, Hickory Point Bank has had the privilege of helping families, businesses, and communities move forward. We are grateful for the confidence you have in us and for the relationships that have grown over many years.

Today, we are writing to share an important announcement about the bank’s future. First Illinois Corporation has entered into a merger agreement with First Financial Corporation, with Hickory Point Bank merging with First Financial Bank, NA. We expect the merger to be completed in the fourth quarter of 2026.

We recognize that news of this nature can feel unexpected, especially when it involves an institution and people you know and trust. We want you to hear directly from us why this decision was made and what it means at this stage.

The decision reflects thoughtful planning and responsible stewardship. Banking continues to change, and greater scale provides the ability to invest in technology, security, talent, products, and client capabilities. We believe this partnership offers a strong path forward while building on the personal service and local relationships that have defined Hickory Point Bank.

For now, please continue to bank with us as you normally do. Your Hickory Point Bank team remains available to serve you and answer questions. If future changes require action from you, we will communicate clearly and in advance.

We are excited about the additional scale and resources that this merger will bring to our clients. Founded in 1834, First Financial Bank, NA is one of the oldest community banks in the nation. Headquartered in Terre Haute, Indiana, First Financial shares our commitment to local, relationship-based community banking.

Thank you for your trust and your relationship. We will continue to keep you informed as this process moves forward.

With gratitude,

Anthony G. Nestler

President & CEO

Important Additional Information About the Merger and Where to Find It

In connection with the proposed transaction, First Financial will file materials with the SEC, including a registration statement on Form S-4. The registration statement will include a proxy statement of First Illinois that also constitutes a prospectus of First Financial, which will be sent to the shareholders of First Illinois. This communication is not a substitute for the proxy statement/prospectus or the registration statement or for any other document that First Financial may file with the SEC and send to First Illinois’ shareholders in connection with the proposed transaction. FIRST ILLINOIS’ SHAREHOLDERS ARE URGED TO CAREFULLY AND THOROUGHLY READ THE PROXY STATEMENT/PROSPECTUS AND THE REGISTRATION STATEMENT, AS MAY BE AMENDED OR SUPPLEMENTED FROM TIME TO TIME, AND OTHER RELEVANT DOCUMENTS FILED BY FIRST FINANCIAL WITH THE SEC, WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT FIRST FINANCIAL, FIRST ILLINOIS, THE PROPOSED TRANSACTION, THE RISKS RELATED THERETO AND OTHER MATTERS.

When filed, the registration statement and other documents relating to the merger filed by First Financial can be obtained free of charge from the SEC’s website at www.sec.gov. These documents also can be obtained free of charge by accessing First Financial’s website at https://investor.first-online.bank under the “Investor Relations” section. Alternatively, these documents, when available, can be obtained free of charge from First Financial upon written request to First Financial Corporation, Attn: Norman D. Lowery, President and CEO, One First Financial Plaza, Terre Haute, Indiana 47807 or by calling 812-238-6185. The contents of the website referenced above are not deemed to be incorporated by reference into the registration statement or the proxy statement/prospectus.

Participants in the Solicitation

First Financial, First Illinois and their respective directors, executive officers, and certain other persons may be deemed, under SEC rules, to be participants in the solicitation of proxies from First Illinois’ shareholders in connection with the proposed merger. Information regarding the directors and executive officers of First Financial is included in its definitive proxy statement for its 2026 annual meeting filed with the SEC on March 17, 2026. Information regarding the directors and executive officers of First Illinois and additional information regarding the persons who may be deemed participants and their direct and indirect interests, by security holdings or otherwise, will be set forth in the registration statement on Form S-4 and other materials when they are filed by First Financial with the SEC in connection with the proposed transaction. Free copies of these documents may be obtained as described in the section above.

No Offer or Solicitation

This communication does not constitute an offer to sell or the solicitation of an offer to buy securities nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of such jurisdiction. This communication is also not a solicitation of any vote in any jurisdiction pursuant to the proposed merger or otherwise. No offer of securities or solicitation will be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act of 1933, as amended.