CFO — Gerald J. Ritzert: The filing discloses the execution of a supplemental executive retirement plan participation agreement, which is a compensatory arrangement rather than a change in management status or departure.

of this Current Report on Form 8-K, including Exhibit 99.1 furnished herewith, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or otherwise subject to the liabilities of that section, nor will any of such information be deemed incorporated by reference into any filing made by the registrant under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific referen…

Entry Into a Material Definitive Agreement. On June 16, 2026, Isabella Bank Corporation, a Michigan corporation (the “Company”), and its wholly-owned subsidiary, Isabella Bank, a Michigan state-chartered bank (the “Bank”), entered into an Equity Distribution Agreement (the “Agreement”) with Piper Sandler & Co., as sales agent (the “Agent”), pursuant to which the Company may issue and sell from time to time through the Agent, shares of the Company's common stock, no par value per share (the “C…

Entry into a Material Definitive Agreement. On June 11, 2026, Isabella Bank Corporation, a Michigan corporation (“Isabella”), 401 Merger Sub, Inc., a Michigan corporation and a wholly owned subsidiary of Isabella (“Merger Sub”), and Grand River Commerce, Inc., a Michigan corporation (“Grand River”), entered into an Agreement and Plan of Merger (the “Merger Agreement”). The Merger Agreement provides that, upon the terms and subject to the conditions set forth therein, Merger Sub will merge wit…

of this Current Report on Form 8-K, including Exhibit 99.1 furnished herewith, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or otherwise subject to the liabilities of that section, nor will any of such information be deemed incorporated by reference into any filing made by the registrant under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific referen…

Director — Jae A. Evans: Jae A. Evans resigned from the Board of Directors and the Board of Directors of Isabella Bank.

of this Current Report on Form 8-K, including Exhibit 99.1 furnished herewith, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or otherwise subject to the liabilities of that section, nor will any of such information be deemed incorporated by reference into any filing made by the registrant under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific referen…

Chief Financial Officer — Gerald J. Ritzert: Appointment of Gerald J. Ritzert as Chief Financial Officer.

of this Current Report on Form 8-K, including Exhibit 99.1 furnished herewith, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or otherwise subject to the liabilities of that section, nor will any of such information be deemed incorporated by reference into any filing made by the registrant under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific referen…

Director — Brian Tessin: Brian Tessin was appointed as a Director for Isabella Bank Corporation and Isabella Bank.

CFO — William M. Schaefer: Mr. William M. Schaefer was terminated as CFO of Isabella Bank Corporation.

of this Current Report on Form 8-K, including Exhibit 99.1 furnished herewith, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or otherwise subject to the liabilities of that section, nor will any of such information be deemed incorporated by reference into any filing made by the registrant under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific referen…

Director — Chad R. Payton: Mr. Payton resigned from the Board of Directors and all committees without any disagreements.

Other Events . On May 1, 2025, Isabella Bank Corporation (the “Company”) issued a press release announcing that its Board of Directors has approved a share repurchase authorization of an additional five hundred thousand (500,000) common shares, pursuant to the Company's publicly announced common stock repurchase plan. Authorizations do not have expiration dates. As common shares are repurchased under this plan, they are retired and revert back to the status of authorized, but unissued common…

of Form 8-K and Exhibit 99.1 attached hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, nor shall it be deemed incorporated by reference in any filing made by the registrant under the Securities Act of 1933, whether made before or after the date hereof, except as shall be expressly set forth by specific reference in such filing. Section 9 - Financial Statements and Exhibits

The filing details changes to compensation and retirement plans, not a management change.

Director — David B. Behen: David B. Behen was appointed as a Director for Isabella Bank Corporation and Isabella Bank.

Changes in Registrant's Certifying Accountant. (b) Engagement of New Independent Registered Public Accounting Firm As previously reported by Isabella Bank Corporation (the "Corporation") on Form 8-K filed with the Securities and Exchange Commission on March 8, 2024, Rehmann Robson, LLC resigned as the independent registered public accounting firm of the Corporation, effective after completion of their audits of the Corporation's consolidated financial statements as of and for the year ending…

of Form 8-K and Exhibit 99.1 attached hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, nor shall it be deemed incorporated by reference in any filing made by the registrant under the Securities Act of 1933, whether made before or after the date hereof, except as shall be expressly set forth by specific reference in such filing. Section 9 - Financial Statements and Exhibits

Other Events . On November 21, 2024, the Corporation filed a Form 8-K stating that a press release was issued on November 21, 2024 announcing that its Board of Directors declared a twenty-eight cent ($0.28) per common share fourth quarter cash dividend, payable December 18, 2024 to shareholders of record as of December 16, 2024. This Current Report on Form 8-K/A is solely being filed to clarify that the press release referenced above was not issued. The Corporation has furnished a copy of the…

of Form 8-K and Exhibit 99.1 attached hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, nor shall it be deemed incorporated by reference in any filing made by the registrant under the Securities Act of 1933, whether made before or after the date hereof, except as shall be expressly set forth by specific reference in such filing. Section 9 - Financial Statements and Exhibits

Director — Thomas L. Kleinhardt and Gregory V. Varner: Directors retired due to mandatory age for retirement according to the Corporation’s bylaws.

Director — Brian R. Sackett: Brian R. Sackett was appointed as a new Director to the Board of Isabella Bank Corporation and Isabella Bank.

CFO — William Schaefer: Compensatory arrangements and retirement plan updates for the CFO.

of Form 8-K and Exhibit 99.1 attached hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, nor shall it be deemed incorporated by reference in any filing made by the registrant under the Securities Act of 1933, whether made before or after the date hereof, except as shall be expressly set forth by specific reference in such filing. Section 9 - Financial Statements and Exhibits