NICOLET BANKSHARES INC

(Former name or former address, if changed since last report)

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Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter.)

Emerging Growth Company☐

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On October 23, 2025, Nicolet Bankshares, Inc. (“Nicolet”) and MidWest One Financial Group, Inc. (“MidWest One”) entered into an Agreement and Plan of Merger (the “Merger Agreement”), pursuant to which MidWest One will merge with and into Nicolet (the “Merger”).

Nicolet and MidWest One have agreed to prepare and file with the Securities and Exchange Commission a registration statement on Form S-4, which will include a proxy statement/prospectus to be mailed to both Nicolet and MidWest One shareholders. As soon as practicable following effectiveness of the registration statement on Form S-4, Nicolet and MidWest One will each call a special shareholder meeting to approve the Merger Agreement.

Merger Consideration: Pursuant to the terms and subject to the conditions set forth in the Merger Agreement, Nicolet will exchange shares of its common stock for all of the outstanding shares of MidWest One common stock, in an all-stock transaction. MidWest One shareholders will be entitled to receive 0.3175 of a share of Nicolet common stock for each share of MidWest One common stock they own upon the effective time of the merger, for aggregate merger consideration valued at approximately $864 million, or $41.37 per share, based on Nicolet’s closing stock price of $130.31 as of October 22, 2025. Upon completion of the merger, the shares issued to MidWest Oneshareholders are expected to comprise 30% of the outstanding shares of the combined company.

Closing Conditions: Consummation of the Merger is subject to certain customary closing conditions, including without limitation, (i) approval of the Merger Agreement by both Nicolet and MidWest One shareholders, (ii) the receipt of all requisite regulatory approvals, and (iii) receipt of a tax opinion of Nicolet’s counsel that the Merger will qualify as a tax-free reorganization.

Representations, Warranties and Covenants: The Merger Agreement includes detailed representations, warranties and covenant

provisions that are customary for transactions of this type.

The foregoing description of the Merger Agreement does not purport to be complete and is qualified in its entirety by reference

to the full text of the Merger Agreement, a copy of which is attached hereto as Exhibit 2.1.

The representations and warranties set forth in the Merger Agreement have been made solely for the benefit of the parties to the

Merger Agreement. In addition, such representations and warranties (i) have been made only for the purpose of the Merger Agreement; (ii) have been qualified by the disclosures made to the other party in connection with the Merger Agreement; (iii) are subject to materiality qualifications contained in the Merger Agreement, which may differ from what may be viewed as material by investors; and (iv) have been included in the Merger Agreement for the purpose of allocating risk between the contracting parties and not for the purpose of establishing such matters as facts. Based upon the foregoing reasons, you should not rely on the representations and warranties as statements of factual information. Investors should read the Merger Agreement together with the other information concerning Nicolet and MidWest One that is in reports and statements filed with the SEC.

On October 23, 2025, Nicolet Bankshares, Inc. (“Nicolet”) and MidWest One Financial Group, Inc. (“MidWest One”) jointly announced the execution of a definitive merger agreement pursuant to which, upon the terms and subject to the conditions set forth therein, Nicolet will acquire MidWest One and its wholly-owned banking subsidiary MidWest One Bank. A copy of the press release is furnished as Exhibit 99.1 to this Current Report on Form 8-K.

In connection with the announcement of the Merger Agreement, Nicolet and MidWest One intend to provide supplemental information regarding the proposed transaction in connection with presentations to analysts and investors. A copy of the joint investor presentation is furnished as Exhibit 99.2 to this Current Report on Form 8-K.

The Merger Agreement was unanimously approved by the board of directors of each company. It is subject to shareholder approval of each company, regulatory approvals, and other customary closing conditions. The Merger is expected to close in the first half of 2026.

Forward Looking Statements “Safe Harbor” Statement Under the Private Securities Litigation Reform Act of 1995.

This communication contains statements that constitute “forward-looking statements” within the meaning, and subject to the protections of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. All statements other than statements of historical fact are forward-looking statements. Such statements include, statements related to the expected timing of the completion of the proposed transaction. You can identify these forward-looking statements through the use of words such as “anticipate,” “believe,” “assume,” “aim,” “can,” “conclude,” “continue,” “could,” “estimate,” “expect,” “foresee,” “goal,” “intend,” “may,” “might,” “outlook,” “possible,” “plan,” “predict,” “project,” “potential,” “seek,” “should,” “target,” “will,” “will likely,” “would,” or the negative of these terms or other comparable terminology.

A number of factors could cause actual results and outcomes to differ materially from those contemplated by these forward-looking statements. These factors include, but are not limited to: (1) the parties’ inability to meet expectations regarding the timing of the proposed merger; (2) the failure to obtain the necessary approvals by the shareholders of Nicolet or MidWest One; (3) the ability by each of Nicolet and MidWest One to obtain required governmental approvals of the proposed transaction on the timeline expected (which could be affected by government shutdowns), or at all, and the risk that such approvals may result in the imposition of conditions that could adversely affect the combined company after the closing of the proposed transaction or adversely affect the expected benefits of the proposed transaction; (4) the failure to satisfy other conditions to completion of the proposed merger, or any unexpected delay in closing the proposed transaction or the occurrence of any event, change or other circumstances that could give rise to the termination of the merger agreement; and (5) the outcome of any legal or regulatory proceedings or governmental inquiries or investigations that may be currently pending or later instituted against Nicolet or MidWest One.

All forward-looking statements included in this communication are made as of the date hereof and are based on information available to management at that time. Except as required by law, neither Nicolet nor MidWest Oneassumes any obligation to update any forward-looking statement to reflect events or circumstances that occur after the date the forward-looking statements were made.