(NASDAQ:OSBC) Exhibit 99.1 Contact: Bradley S. Adams For Immediate Release Chief Financial Officer April 17, 2024 (630) 906-5484 Old Second Bancorp, Inc. Reports First Quarter 2024 Net Income of $21.3 Million, or$0.47 per Diluted Share AURORA, IL, April 17, 2024 – Old Second Bancorp, Inc. (the “Company,” “Old Second,” “we,” “us,” and “our”) (NASDAQ: OSBC), the parent company of Old Second National Bank (the “Bank”), today announced financial results for the first quarter of 2024. Our net income was $21.3 m ...