<SEC-HEADER>0001144204-17-008715.hdr.sgml : 20170214
<ACCEPTANCE-DATETIME>20170214152723
ACCESSION NUMBER:		0001144204-17-008715
CONFORMED SUBMISSION TYPE:	SC 13G
PUBLIC DOCUMENT COUNT:		1
FILED AS OF DATE:		20170214
DATE AS OF CHANGE:		20170214

SUBJECT COMPANY:	

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Six Flags Entertainment Corp
		CENTRAL INDEX KEY:			0000701374
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-MISCELLANEOUS AMUSEMENT & RECREATION [7990]
		IRS NUMBER:				133995059
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		SC 13G
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	005-33593
		FILM NUMBER:		17607911

	BUSINESS ADDRESS:	
		STREET 1:		924 AVENUE J EAST
		CITY:			GRAND PRAIRIE
		STATE:			TX
		ZIP:			75050
		BUSINESS PHONE:		972 595-5000

	MAIL ADDRESS:	
		STREET 1:		924 AVENUE J EAST
		CITY:			GRAND PRAIRIE
		STATE:			TX
		ZIP:			75050

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	SIX FLAGS, INC.
		DATE OF NAME CHANGE:	20070322

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	SIX FLAGS INC
		DATE OF NAME CHANGE:	20000714

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	TIERCO GROUP INC/DE/
		DATE OF NAME CHANGE:	19920703

FILED BY:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			WILLIAM BLAIR INVESTMENT MANAGEMENT, LLC
		CENTRAL INDEX KEY:			0001644956
		IRS NUMBER:				472614791
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		SC 13G

	BUSINESS ADDRESS:	
		STREET 1:		222 WEST ADAMS STREET
		CITY:			CHICAGO
		STATE:			IL
		ZIP:			60606
		BUSINESS PHONE:		312-236-1600

	MAIL ADDRESS:	
		STREET 1:		222 WEST ADAMS STREET
		CITY:			CHICAGO
		STATE:			IL
		ZIP:			60606
</SEC-HEADER>