Turkish Airlines flights usually arrive at and depart from the following terminal (Note: Arrival and departure terminals can and do change for various reasons - always check the arrival and departure screens in the airport)
Passengers traveling into IAH on international flights will arrive at gates in either Terminal D or Terminal E. They will disembark and make their way through secure corridors and across the sky bridges to the adjoining Federal Inspection Services (FIS). Here they will clear Immigration and Passport Control, go downstairs, claim baggage, and clear customs.
Terminal - d is used in Houston. Visit : https://www.airlinesairportsterminal.com/turkish-airlines/turkish-airlines-george-bush-intercontinental-airport-iah-terminal/