Wondering What Terminal is Southwest Airlines at STL? Southwest Airlines operates out of Terminal 2 at St. Louis Lambert International Airport. This modern and efficient terminal is exclusively used by Southwest, making it easy for travelers to navigate. Terminal 2 features streamlined check-in services, TSA security checkpoints, and convenient gate access, ensuring a smooth travel experience. Passengers can also enjoy a variety of dining options, retail stores, and free Wi-Fi while waiting for their flight. Whether you're flying for business or leisure, Southwest Airlines at STL helps you plan ahead and travel with ease.