<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2014-09-15</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000101199</issuerCik>
        <issuerName>UNITED FIRE GROUP INC</issuerName>
        <issuerTradingSymbol>UFCS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001515002</rptOwnerCik>
            <rptOwnerName>Sheeley Michael J.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>118 SECOND AVENUE SE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CEDAR RAPIDS</rptOwnerCity>
            <rptOwnerState>IA</rptOwnerState>
            <rptOwnerZipCode>52407-3909</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>VP/COO - United Life Ins. Co.</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2014-09-15</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value>E</value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>7</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>28.5213</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4024</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2014-09-16</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value>E</value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>28.49</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4026</value>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Shares acquired through participation in the Issuer's Dividend Reinvestment Plan.</footnote>
        <footnote id="F2">Represents the approximate number of shares (excluding fractionals) acquired by the Reporting Person through the Issuer's Dividend Reinvestment Plan.</footnote>
        <footnote id="F3">The total number of securities beneficially held directly by the Reporting Person (excluding fractionals)  includes: 1,281 shares held directly by Mr. Sheeley; 1,033 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/15/2018; and 1,710 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/21/2019.</footnote>
        <footnote id="F4">The total number of securities beneficially held directly by the Reporting Person (excluding fractionals)  includes: 1,283 shares held directly by Mr. Sheeley; 1,033 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/15/2018; and 1,710 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/21/2019.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Michael J. Sheeley by Dianne M. Lyons, Attorney-in-Fact</signatureName>
        <signatureDate>2014-09-19</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2014-09-15
0
0000101199
UNITED FIRE GROUP INC
UFCS
0001515002
Sheeley Michael J.
118 SECOND AVENUE SE
CEDAR RAPIDS
IA
52407-3909
0
1
0
0
VP/COO - United Life Ins. Co.
Common Stock
2014-09-15
5
J
0
E
7
28.5213
A
4024
D
Common Stock
2014-09-16
5
J
0
E
2
28.49
A
4026
D
Shares acquired through participation in the Issuer's Dividend Reinvestment Plan.
Represents the approximate number of shares (excluding fractionals) acquired by the Reporting Person through the Issuer's Dividend Reinvestment Plan.
The total number of securities beneficially held directly by the Reporting Person (excluding fractionals)  includes: 1,281 shares held directly by Mr. Sheeley; 1,033 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/15/2018; and 1,710 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/21/2019.
The total number of securities beneficially held directly by the Reporting Person (excluding fractionals)  includes: 1,283 shares held directly by Mr. Sheeley; 1,033 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/15/2018; and 1,710 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/21/2019.
/s/ Michael J. Sheeley by Dianne M. Lyons, Attorney-in-Fact
2014-09-19