Results of Operations and Financial Condition ​ On July 22, 2026, Old Second Bancorp, Inc. (the “Company’s”) issued a press release announcing its financial results for the second quarter ended June 30, 2026, along with certain other financial information. Copies of the Company’s press release and loan portfolio disclosures are attached as Exhibits 99.1 and 99.2, respectively. ​ ​

Director — John Williams, Jr.: Mr. Williams, Jr. resigned from the Board due to reaching the age of 73 as per the Company's Director Resignation Policy.

Other Events. ​ The Board of Directors of Old Second Bancorp, Inc. (the “Company”) has authorized a new share repurchase program under which the Company may repurchase up to $61.2 million of additional shares of the Company’s common stock from July 1, 2026 through June 30, 2027 (the “Repurchase Program”). The Company has received nonobjection from the Federal Reserve Bank of Chicago to the Repurchase Program. ​ Repurchases by the Company under the Repurchase Program may be made from time to t…

Director — Dennis Klaeser: Mr. Klaeser resigned from the Board and Bank Board.

Results of Operations and Financial Condition ​ On April 22, 2026, Old Second Bancorp, Inc. (the “Company’s”) issued a press release announcing its financial results for the first quarter ended March 31, 2026, along with certain other financial information. Copies of the Company’s press release and loan portfolio disclosures are attached as Exhibits 99.1 and 99.2, respectively. ​ ​

Other Events. ​ The Board of Directors of Old Second Bancorp, Inc. (the “Company”) has authorized the repurchase of up to $43.9 million of shares of the Company’s common stock (the “Repurchase Program”). On January 27, 2026, the Company received a letter from the Federal Reserve Bank of Chicago (the “Federal Reserve”) dated January 8, 2026, indicating its nonobjection to the Repurchase Program. Repurchases by the Company under the Repurchase Program may be made from time to time through open…

Results of Operations and Financial Condition ​ On January 21, 2026, Old Second Bancorp, Inc. (the “Company’s”) issued a press release announcing its financial results for the fourth quarter ended December 31, 2025, along with certain other financial information. Copies of the Company’s press release and loan portfolio disclosures are attached as Exhibits 99.1 and 99.2, respectively. ​ ​

Results of Operations and Financial Condition ​ On October 22, 2025, Old Second Bancorp, Inc. (the “Company’s”) issued a press release announcing its financial results for the third quarter ended September 30, 2025, along with certain other financial information. Copies of the Company’s press release and loan portfolio disclosures are attached as Exhibits 99.1 and 99.2, respectively. ​ ​

Director — John Ladowicz: Mr. Ladowicz resigned from the Board due to reaching the age of 73 as per the Company's Director Resignation Policy.

Results of Operations and Financial Condition ​ On July 23, 2025, Old Second Bancorp, Inc. (the “Company’s”) issued a press release announcing its financial results for the second quarter ended June 30, 2025, along with certain other financial information. Copies of the Company’s press release and loan portfolio disclosures are attached as Exhibits 99.1 and 99.2, respectively. ​ ​

Regulation FD Disclosure. ​ On June 18, 2025, Bancorp Financial, Inc. (“ Bancorp Financial ”) received stockholder approval for the previously announced merger of Bancorp Financial with and into Old Second Bancorp, Inc. (the “ Merger ”). The Merger, which was announced on February 25, 2025, is expected to close on July 1, 2025, subject to satisfaction of customary closing conditions. ​ Cautionary Note Regarding Forward-Looking Statements ​ This Current Report on Form 8-K (the “ Report ”) cont…

Results of Operations and Financial Condition ​ On April 23, 2025, Old Second Bancorp, Inc. (the “Company’s”) issued a press release announcing its financial results for the first quarter ended March 31, 2025, along with certain other financial information. Copies of the Company’s press release and loan portfolio disclosures are attached as Exhibits 99.1 and 99.2, respectively. ​ ​

Other Events. ​ On February 25, 2025, Old Second and Bancorp Financial issued a joint press release announcing the execution of the Merger Agreement. A copy of the press release is filed as Exhibit 99.1 hereto and is incorporated herein by reference. ​ Old Second will conduct a live conference call to discuss the Merger today, February 25, 2025, at 11:00 a.m. Eastern Time (10:00 a.m. Central Time). To listen to the live call, please dial 888-506-0062, using Entry Code: 146201. Investors shoul…

Entry into a Definitive Material Agreement. ​ On February 24, 2025, Old Second Bancorp, Inc. (“ Old Second ”) and Bancorp Financial, Inc. (“ Bancorp Financial ”) 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, Bancorp Financial will merge with and into Old Second, with Old Second continuing as the surviving entity (the “ Merger ”). Immediately following the Merger, Ever…

Results of Operations and Financial Condition ​ On January 22, 2025, Old Second Bancorp, Inc. (the “Company’s”) issued a press release announcing its financial results for the fourth quarter ended December 31, 2024, along with certain other financial information. Copies of the Company’s press release and loan portfolio disclosures are attached as Exhibits 99.1 and 99.2, respectively. ​ ​

Other Events. ​ The Board of Directors of Old Second Bancorp, Inc. (the “Company”) has authorized the repurchase of up to $39.1 million of shares of the Company’s common stock (the “Repurchase Program”). On December 16, 2024, the Federal Reserve Bank of Chicago (the “Federal Reserve”) informed us of their non-objection for the Repurchase Program. Repurchases by the Company under the Repurchase Program may be made from time to time through open market purchases, trading plans established in ac…

Other Events. ​ The Board of Directors of Old Second Bancorp, Inc. (the “Company”) has authorized the repurchase of up to $39.1 million of shares of the Company’s common stock (the “Repurchase Program”). On December 16, 2024, the Federal Reserve Bank of Chicago (the “Federal Reserve”) informed us of their non-objection for the Repurchase Program. Repurchases by the Company under the Repurchase Program may be made from time to time through open market purchases, trading plans established in ac…

Regulation FD Disclosure. ​ On December 6, 2024, Old Second Bancorp, Inc. (the “Company”), the parent of Old Second National Bank (the “Bank”), issued a press release announcing the closing of the Bank’s branch purchase and assumption agreement with First Merchants Bank (“First Merchants”) pursuant to which Old Second National Bank acquired from First Merchants certain assets and assumed certain liabilities of five bank branches located in the greater Chicago, Illinois MSA. ​ A copy of the pr…

Results of Operations and Financial Condition ​ On October 16, 2024, Old Second Bancorp, Inc. (the “Company’s”) issued a press release announcing its financial results for the third quarter ended September 30, 2024, along with certain other financial information. Copies of the Company’s press release and loan portfolio disclosures are attached as Exhibits 99.1 and 99.2, respectively. ​ ​

Regulation FD Disclosure. ​ On August 27, 2024, Old Second National Bank (the “Bank”), a subsidiary of Old Second Bancorp, Inc. (the “Company”), and First Merchants Bank (“First Merchants”), a subsidiary of First Merchants Corporation, issued a joint press release announcing the signing of a branch purchase and assumption agreement pursuant to which Old Second National Bank will acquire from First Merchants certain assets and assume certain liabilities of five bank branches located in the gre…

Results of Operations and Financial Condition ​ On July 17, 2024, Old Second Bancorp, Inc. (the “Company’s”) issued a press release announcing its financial results for the second quarter ended June 30, 2024, along with certain other financial information. Copies of the Company’s press release and loan portfolio disclosures are attached as Exhibits 99.1 and 99.2, respectively. ​ ​

Results of Operations and Financial Condition ​ On April 17, 2024, Old Second Bancorp, Inc. (the “Company’s”) issued a press release announcing its financial results for the first quarter ended March 31, 2024, along with certain other financial information. Copies of the Company’s press release and loan portfolio disclosures are attached as Exhibits 99.1 and 99.2, respectively. ​ ​

Vice Chairman — Gary Collins: The filing discloses a new employment agreement for a sitting Vice Chairman that transitions him from direct management to a strategic advisory role, rather than a departure.