The Ontario Airport Southwest Terminal, located in Ontario, California, is a state-of-the-art facility that serves as a major hub for Southwest Airlines. Southwest Airlines uses Terminal 4 at Ontario International Airport (ONT). Terminal 4 is located on the west side of the airport, across the airfield from Terminal 2.

Passengers can walk between Terminals 2 and 4, but it is a long walk (about 1.5 miles). There is also a free shuttle service that runs between the terminals every 15 minutes.

The shuttle stop for Terminal 4 is located outside the baggage claim area. The shuttle stop for Terminal 2 is located outside the ticketing area.