What terminal is Southwest Airlines at Ontario airport ?

Passengers have access to the online / mobile / web check-in option via the Southwest.com® or the Southwest® app, this is available from 24 hours up to 1 hour before a flight's scheduled time of departure.

Passengers may even opt to check-in at the Southwest Airlines Ontario airport terminal at the counter; check-in at the airport counter stops 60 minutes before a flight's scheduled departure time