    <SEC-DOCUMENT>0000357173-23-000078-index.html : 20231018
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    <ACCEPTANCE-DATETIME>20231018160017
    ACCESSION NUMBER:		0000357173-23-000078
    CONFORMED SUBMISSION TYPE:	8-K
    PUBLIC DOCUMENT COUNT:		22
    CONFORMED PERIOD OF REPORT:	20231018
    ITEM INFORMATION:		Results of Operations and Financial Condition
    ITEM INFORMATION:		Financial Statements and Exhibits
    FILED AS OF DATE:		20231018
    DATE AS OF CHANGE:		20231018

    FILER:

    	COMPANY DATA:
    		COMPANY CONFORMED NAME:			OLD SECOND BANCORP INC
    		CENTRAL INDEX KEY:			0000357173
    		STANDARD INDUSTRIAL CLASSIFICATION:	STATE COMMERCIAL BANKS [6022]
    		IRS NUMBER:				363143493
    		STATE OF INCORPORATION:			DE
    		FISCAL YEAR END:			1231

    	FILING VALUES:
    		FORM TYPE:		8-K
    		SEC ACT:		1934 Act
    		SEC FILE NUMBER:	000-10537
    		FILM NUMBER:		231332215

    	BUSINESS ADDRESS:
    		STREET 1:		37 S RIVER ST
    		CITY:			AURORA
    		STATE:			IL
    		ZIP:			60507
    		BUSINESS PHONE:		6308920202

    	MAIL ADDRESS:
    		STREET 1:		37 SOUTH RIVER STREET
    		CITY:			AURORA
    		STATE:			IL
    		ZIP:			60507
    </SEC-HEADER>
    <DOCUMENT>
    <TYPE>8-K
    <SEQUENCE>1
    <FILENAME>tmb-20231018x8k.htm
    <DESCRIPTION>8-K
    <TEXT>
    Document 1 - file: tmb-20231018x8k.htm

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    <TYPE>EX-99.1
    <SEQUENCE>2
    <FILENAME>tmb-20231018xex99d1.htm
    <DESCRIPTION>EX-99.1
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    Document 2 - file: tmb-20231018xex99d1.htm

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    <SEQUENCE>3
    <FILENAME>tmb-20231018xex99d2.htm
    <DESCRIPTION>EX-99.2
    <TEXT>
    Document 3 - file: tmb-20231018xex99d2.htm

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    <DESCRIPTION>GRAPHIC
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    Document 4 - file: tmb-20231018x8k001.jpg

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    <FILENAME>tmb-20231018xex99d2001.jpg
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    Document 6 - file: tmb-20231018xex99d2001.jpg

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    <FILENAME>tmb-20231018xex99d2002.jpg
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    Document 7 - file: tmb-20231018xex99d2002.jpg

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    Document 8 - file: tmb-20231018xex99d2003.jpg

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    <FILENAME>tmb-20231018xex99d2004.jpg
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    Document 9 - file: tmb-20231018xex99d2004.jpg

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    <FILENAME>tmb-20231018xex99d2005.jpg
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    Document 10 - file: tmb-20231018xex99d2005.jpg

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    <DOCUMENT>
    <TYPE>EX-101.SCH
    <SEQUENCE>11
    <FILENAME>tmb-20231018.xsd
    <DESCRIPTION>EX-101.SCH
    <TEXT>
    Document 11 - file: tmb-20231018.xsd

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    <DOCUMENT>
    <TYPE>EX-101.LAB
    <SEQUENCE>12
    <FILENAME>tmb-20231018_lab.xml
    <DESCRIPTION>EX-101.LAB
    <TEXT>
    Document 12 - file: tmb-20231018_lab.xml

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    <DOCUMENT>
    <TYPE>EX-101.PRE
    <SEQUENCE>13
    <FILENAME>tmb-20231018_pre.xml
    <DESCRIPTION>EX-101.PRE
    <TEXT>
    Document 13 - file: tmb-20231018_pre.xml

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    <TYPE>XML
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    <SEQUENCE>15
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    Document 15 - file: R2.htm

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    <FILENAME>tmb-20231018x8k_htm.xml
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    Document 16 - RAW XML: tmb-20231018x8k_htm.xml

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    <DOCUMENT>
    <TYPE>EXCEL
    <SEQUENCE>17
    <FILENAME>Financial_Report.xlsx
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    <TEXT>
    Document 17 - file: Financial_Report.xlsx

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    <TYPE>XML
    <SEQUENCE>18
    <FILENAME>Show.js
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    <TEXT>
    Document 18 - file: Show.js

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    <TYPE>XML
    <SEQUENCE>19
    <FILENAME>report.css
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    <TEXT>
    Document 19 - file: report.css

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    <DOCUMENT>
    <TYPE>XML
    <SEQUENCE>20
    <FILENAME>FilingSummary.xml
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    Document 20 - file: FilingSummary.html

    Document 20 - RAW XML: FilingSummary.xml

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    <DOCUMENT>
    <TYPE>JSON
    <SEQUENCE>23
    <FILENAME>MetaLinks.json
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    Document 23 - file: MetaLinks.json

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    <TYPE>ZIP
    <SEQUENCE>24
    <FILENAME>0000357173-23-000078-xbrl.zip
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    Document 24 - file: 0000357173-23-000078-xbrl.zip

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