EX-5.1 3 isba_8kx2026xatmxexhibitx51.htm EX-5.1

EXHIBIT 5.1

Lansing 313 S. Washington Square Lansing MI 48933 Detroit 333 W. Fort Street – Suite 1400 Detroit MI 48226

Southfield 28411 Northwestern Highway, Suite 500 Southfield MI 48034 Holland 151 Central Avenue - Suite 260 Holland MI 49423

Grand Rapids 1700 E. Beltline NE - Suite 200 Grand Rapids MI 49525

Walter S. Foster      1878-1961 Richard B. Foster      1908-1996 Theodore W. Swift      1928-2000 John L. Collins      1926-2001 Webb A. Smith      1938-2025 Charles A. Janssen Charles E. Barbieri Brent A. Titus Brian G. Goodenough Matt G. Hrebec Deanna Swisher Thomas R. Meagher Douglas A. Mielock

Scott A. Chernich Paul J. Millenbach Dirk H. Beckwith Brian J. Renaud Lynwood P. VandenBosch Lawrence Korolewicz James B. Doezema Anne M. Seurynck Michael D. Homier Scott H. Hogan Benjamin J. Price Michael R. Blum Jonathan J. David Andrew C. Vredenburg Julie I. Fershtman Todd W. Hoppe Jennifer B. Van Regenmorter Thomas R. TerMaat Frederick D. Dilley

David R. Russell Joel C. Farrar Laura J. Genovich Karl W. Butterer, Jr. Mindi M. Johnson Ray H. Littleton, II Anna K. Gibson Nicholas M. Oertel Alicia W. Birach Adam A. Fadly Ryan E. Lamb Clifford L. Hammond Matthew S. Fedor Stefania Gismondi Leslie A. Abdoo Julie L. Hamlet Michael C. Zahrt Mark T. Koerner Warren H. Krueger, III

Taylor A. Gast Thomas K. Dillon Robert A. Hamor Jacquelyn A. Dupler Dora A. Brantley James F. Anderton, V Sara L. Cunningham Michael A. Cassar Alexander S. Rusek Amanda J. Dernovshek Brandon M. H. Schumacher Bryan Cermak Kevin J. Roragen Allison M. Collins Alaina M. Nelson Gabrielle C. Lawrence Steven J. Tjapkes Erica E.L. Huddas Jennifer L. Montasir

Mikhail Murshak Courtney G. Agrusa Benjamin M. Williams Rachael Kuilema Klein Michael R. Kluck Kelly Reed Lucas Paula K. Manis Michael G. Oliva Jeffrey S. Theuer Jeffrey G. Schultz Amanda S. Marinkovski Thomas W. Huyck Xavier E. Prather Joseph J. Giacalone Anthony M. Dalimonte Nicholas J. Stock, II Keith T. Brown Mallory E. Reader Dina D. Kashat

Lindsey M. Mead Destiny R. Hughes Samantha D. Shepard McKenna S. Rivers Melanie A. Assad Matthew C. Murray Mackenzie M. Almassian Patrick E. Quinn Charles R. Sarchet Rachel A. Conner Olivia K. Reid Allison N. Shudark Badri Yono, Jr. Lisa V. Gallagher Allison M. Morris Laura A. Kane

Writer's Direct Phone:

517.371.8100

Fax:

517.371.8200

Reply To:

Lansing

June 16, 2026

Isabella Bank Corporation

401 North Main Street

Mt. Pleasant, MI 48858

Dear Ladies and Gentlemen:

We have acted as Michigan counsel to Isabella Bank Corporation, Inc., a Michigan corporation (the “Company”), in connection with the issuance and sale by the Company of shares of the Company’s common stock, no par value (the “Common Stock”), having an aggregate gross sales price not to exceed $30,000,000 (the “Shares”). The Shares may be sold pursuant to the Equity Distribution Agreement, dated as of June 16, 2026 (the “Agreement”), by and among the Company, Isabella Bank, a Michigan banking corporation and wholly-owned subsidiary of the Company (the “Bank”), and Piper Sandler & Co., as sales agent (the “Agent”). The offer and sale of the Shares have been registered under the Securities Act of 1933, as amended (the “Securities Act”) pursuant to a shelf registration statement on Form S-3 filed by the Company with the Securities and Exchange Commission (the “SEC”) on April 16, 2026 (File No. 333-295098) (“the “Registration Statement”), and including the base prospectus included in such Registration Statement (the “Base Prospectus”) and a prospectus supplement relating to the Shares dated June 16, 2026 (the “Prospectus Supplement,” and together with the Base Prospectus, the “Prospectus”).

In rendering the opinions set forth below, we have examined and relied on originals or copies, certified or otherwise identified to our satisfaction, of the Agreement, the Registration Statement, the Prospectus, the Company’s articles of incorporation, as amended (“Articles of Incorporation”), and the Company’s

June 16, 2026

Page 2

Second Amended and Restated Bylaws, resolutions of the Company’s Board of Directors, certificates of public officials, certificates of corporate officers and such other documents and corporate records as we have deemed appropriate for the purpose of rendering this opinion. We have assumed without investigation the genuineness of all signatures, the legal capacity of natural persons, the authenticity, accuracy and completeness of all documents submitted to us as originals, the conformity to authentic and complete original documents of all documents submitted to us as certified, conformed or photostatic copies and the authenticity, accuracy and completeness of the originals of such copies. We have further assumed the due authorization of such documents by all parties other than the Company and the taking of all requisite action respecting such documents by all parties other than the Company, the due execution and delivery of such documents by each party other than the Company and that all agreements are valid and binding agreements of all parties to such agreements, other than the Company. In addition, we have assumed the accuracy of certifications of public officials, government agencies and departments, corporate officers and other individuals on which we are relying, and have made no independent investigations thereof.

The opinions expressed below assume that: (i) upon the issuance of any of the Shares, the total number of shares of Common Stock issued and outstanding will not exceed the total number of shares of Common Stock that the Company is then authorized to issue under its Articles of Incorporation; (ii) the number of Shares, and the sales price of each Share, to be issued by the Company will be determined in accordance with the Agreement and the authorizing resolutions of the Company’s Board of Directors; and (iii) the issuance of the Shares does not require the approval of the Company’s shareholders under the rules of the Nasdaq Stock Market or any other exchange or quotation system on which the Common Stock is then listed or quoted.

Based upon the foregoing, and subject to limitations, qualifications, exceptions and assumptions set forth herein, we are of the opinion that the Shares have been duly authorized and, when issued and delivered as provided in the Agreement and upon receipt by the Company of the consideration therefor as contemplated by the Agreement, will be validly issued, fully paid and non-assessable.

The opinions expressed in this opinion letter are limited to the laws of the State of Michigan. Our opinions are based on these laws as in effect on the date hereof. We express no opinion as to whether the laws of any other jurisdiction are applicable to the subject matter hereof. We are not opining on, and we assume no responsibility for, the applicability for, the applicability to or effect on any of the matters covered herein of the laws of any other jurisdiction. We are not rendering any opinion as to compliance with any federal or state law, rule or regulation relating to securities, or to the sale or issuance thereof.

We hereby consent to the filing of this opinion as an exhibit to the Company’s Current Report on Form 8-K filed on June 16, 2026, and to the reference to our firm under the heading “Legal Matters” in the Prospectus. In giving our consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the SEC thereunder.

June 16, 2026

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Sincerely,

FOSTER, SWIFT, COLLINS & SMITH, P.C.

/s/ Foster, Swift, Collins & Smith, P.C.