<SEC-DOCUMENT>0001179110-18-005772.txt : 20180418
<SEC-HEADER>0001179110-18-005772.hdr.sgml : 20180418
<ACCEPTANCE-DATETIME>20180418174515
ACCESSION NUMBER:		0001179110-18-005772
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20180417
FILED AS OF DATE:		20180418
DATE AS OF CHANGE:		20180418

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			MCLEAN HUGH H
		CENTRAL INDEX KEY:			0001184764

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-10537
		FILM NUMBER:		18762037

	MAIL ADDRESS:	
		STREET 1:		408 S. PROSPECT AVE
		CITY:			ELMHURST
		STATE:			IL
		ZIP:			60126

ISSUER:		

	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:			1215

	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>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4 -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2018-04-17</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000357173</issuerCik>
        <issuerName>OLD SECOND BANCORP INC</issuerName>
        <issuerTradingSymbol>OSBC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001184764</rptOwnerCik>
            <rptOwnerName>MCLEAN HUGH H</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>37 S. RIVER ST.</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>AURORA</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60506</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Old Second Bancorp, Inc. Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2018-04-17</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>5000</value>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>134000</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Included in this total are 125,000 shares  held jointly with spouse, 4,000 shares are restricted stock units and 5,000 shares are Performance Based restricted stock units in Mr. McLean's name alone.</footnote>
        <footnote id="F2">Does not apply.</footnote>
        <footnote id="F3">These shares represent Performance Based Restricted Stock Units granted in 2018 under the Long Term Incentive Program. These shares have a 3-year cliff vesting.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Hugh McLean</signatureName>
        <signatureDate>2018-04-17</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
