You'll be pleased to hear that all Southwest flights are operated out of Terminal 2 at St. Louis Lambert International Airport, if you've ever wondered What terminal is Southwest at STL. Southwest is the only airline using this terminal, which expedites boarding, security, and check-in. Terminal 2 is a favorite among domestic travelers due to its effective layout and traveler-friendly amenities like quick-service food and accessible gate areas. visit : https://airlinesairportterminals.com/southwest-airlines/southwest-airlines-st-louis-lambert-international-airport-stl-terminal/