Allegheny County Airport (IATA: AGC, ICAO: KAGC) is in West Mifflin, Pennsylvania, four miles (6 km) southeast of Pittsburgh. It is the fifth busiest airport in Pennsylvania following Philadelphia, Pittsburgh, Allentown, and Harrisburg. The airport is owned by the Allegheny County Airport Authority and is the primary FAA designated reliever airport for Pittsburgh International Airport. Allegheny County Airport was dedicated on September 11, 1931. When it was completed, it was third largest airport in the country, as well as the only hard-surface airport in the country. It was historically the main entrance to metro Pittsburgh via air from its inception up until June, 1952 when Pittsburgh International opened for commercial aviation.