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Document and Entity Information
Jul. 01, 2025
Document and Entity Information [Abstract]  
Document Type 8-K/A
Document Period End Date Jul. 01, 2025
Entity Registrant Name OLD SECOND BANCORP INC
Entity Incorporation, State or Country Code DE
Securities Act File Number 000-10537
Entity Tax Identification Number 36-3143493
Entity Address, Address Line One 37 South River Street
Entity Address, City or Town Aurora
Entity Address, State or Province IL
Entity Address, Postal Zip Code 60507
City Area Code 630
Local Phone Number 892-0202
Written Communications false
Soliciting Material false
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Title of 12(b) Security Common Stock
Trading Symbol OSBC
Security Exchange Name NASDAQ
Entity Emerging Growth Company false
Entity Central Index Key 0000357173
Amendment Description On July 1, 2025, Old Second Bancorp, Inc. (“Old Second”) filed a Current Report on Form 8-K (the “Initial Filing”) to report that Old Second had completed its acquisition of Bancorp Financial, Inc. (“Bancorp Financial”), pursuant to the Agreement and Plan of Merger, dated as of February 24, 2025 (the “Merger Agreement”) by and between Old Second and Bancorp Financial. Pursuant to the terms of the Merger Agreement, effective July 1, 2025, Bancorp Financial merged with and into Old Second (the “Merger”), with Old Second continuing as the surviving corporation in the Merger. This Current Report on Form 8-K/A amends the Initial Filing to include unaudited consolidated financial statements of Bancorp Financial as of June 30, 2025 and 2024, and for the six-month periods ended June 30, 2025 and 2024 and related notes and pro forma financial information as of and for the six months ended June 30, 2025, each as required by Item 9.01 of Form 8-K.
Amendment Flag true