What Terminal is Sun Country Airlines at BWI? Based in Baltimore/Washington International Thurgood Marshall Airport (BWI), more precisely in Terminal E, is Sun Country Airlines. Many amenities are available at this terminal, which is primarily used for international flights, to improve the experience for guests. Travelers on Sun Country flights can choose from a range of dining and retail options after checking in at the proper stations and completing security. When your departure date draws near, it's a good idea to arrive early and confirm any updates on your flight or terminal information.