-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
 MFgwCgYEVQgBAQICAf8DSgAwRwJAW2sNKK9AVtBzYZmr6aGjlWyK3XmZv3dTINen
 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 OKISGKLugk2eFRXkCFdfIpZveXgMpJW0fuSQWO1SsHqx1l5cUwwg7faz67zK1XRo
 7hHxImslv5f/ZgRz1+ZzCA==

<SEC-DOCUMENT>0001140361-11-013234.txt : 20110301
<SEC-HEADER>0001140361-11-013234.hdr.sgml : 20110301
<ACCEPTANCE-DATETIME>20110301215755
ACCESSION NUMBER:		0001140361-11-013234
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20110301
FILED AS OF DATE:		20110301
DATE AS OF CHANGE:		20110301

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Hooke James
		CENTRAL INDEX KEY:			0001464426

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-32384
		FILM NUMBER:		11654190

	MAIL ADDRESS:	
		STREET 1:		C/O MACQUARIE INFRASTRUCTURE COMPANY LLC
		STREET 2:		125 WEST 55TH STREET
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10019

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Macquarie Infrastructure CO LLC
		CENTRAL INDEX KEY:			0001289790
		STANDARD INDUSTRIAL CLASSIFICATION:	WHOLESALE-PETROLEUM & PETROLEUM PRODUCTS (NO BULK STATIONS) [5172]
		IRS NUMBER:				206196808
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		125 WEST 55TH STREET, 22ND FLOOR
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10019
		BUSINESS PHONE:		212-231-1000

	MAIL ADDRESS:	
		STREET 1:		125 WEST 55TH STREET, 22ND FLOOR
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10019

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	Macquarie Infrastructure Assets LLC
		DATE OF NAME CHANGE:	20040510
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-03-01</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001289790</issuerCik>
        <issuerName>Macquarie Infrastructure CO LLC</issuerName>
        <issuerTradingSymbol>MIC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001464426</rptOwnerCik>
            <rptOwnerName>Hooke James</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O MACQUARIE INFRASTRUCTURE COMPANY LLC</rptOwnerStreet1>
            <rptOwnerStreet2>125 WEST 55TH STREET</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Executive Officer</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Limited Liability Company Interests</value>
            </securityTitle>
            <transactionDate>
                <value>2011-03-01</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>2000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>23.96</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>35000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes></footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ James Hooke</signatureName>
        <signatureDate>2011-03-01</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----