MidAmerica St. Louis Airport is a public use airport next to Scott Air Force Base. It is located 18 nautical miles east of downtown St. Louis and 14 nmi east of the central business district of Belleville in St. Clair County, Illinois, United States. Opened in 1997, MidAmerica is the secondary domestic passenger airport for the Greater St. Louis metropolitan area, after the larger St. Louis Lambert International Airport.