What terminal is southwest at ontario? Southwest Airlines operates out of Terminal 4 at Ontario International Airport. Located in the heart of Southern California, Terminal 4 offers a convenient and efficient experience for Southwest passengers. Designed with modern amenities and state-of-the-art facilities, this terminal provides an excellent atmosphere for both departing and arriving travelers. Passengers can expect spacious check-in areas, ample seating options, and a variety of dining and retail establishments to cater to their needs. Additionally, Terminal 4 boasts excellent accessibility with well-marked signs and clear directions throughout the facility to ensure smooth navigation. The airline staff at Southwest is known for their professionalism and efficiency, ensuring that passengers enjoy a seamless travel experience from start to finish. Travelers flying with Southwest at Ontario can be confident in the high-standard services provided within the confines of Terminal 4.