Material Event (Form 8-K)

Item 8.01 Other Events

On March 4, 2026, Old Second Bancorp, Inc. (the "Company") notified U.S. Bank National Association, as paying agent (the "Paying Agent"), of its intention to redeem (the "Redemption"), on April 15, 2026 (the "Redemption Date"), $30,000,000 aggregate principal amount of its outstanding 3.50% Fixed-to-Floating Rate Subordinated Notes due 2031 (CUSIP No. 680277AC4), originally issued on April 6, 2021 (the "Notes"). The Notes will be redeemed at a cash redemption price equal to 100% of the aggregate principal amount of the Notes being redeemed, plus accrued and unpaid interest thereon to, but excluding, the Redemption Date (the "Redemption Price"). Upon completion of the Redemption, $30,000,000 aggregate principal amount of the Notes will remain outstanding.

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The Company has received non-objection from the Federal Reserve Bank of Chicago with respect to the Redemption.

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Payment of the Redemption Price will be made on the Redemption Date only upon presentation and surrender of the Notes to the Paying Agent. Notes held in book-entry form will be redeemed and the Redemption Price paid in accordance with the applicable procedures of The Depository Trust Company. Interest on the Notes called for redemption will cease to accrue on and after the Redemption Date. Notice of redemption will be delivered to the registered holders of the Notes in accordance with the terms governing the Notes.

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