Naval Air Station Joint Reserve Base Willow Grove or NASJRB Willow Grove (IATA: NXX, ICAO: KNXX, FAA LID: NXX) was a Naval Air Station owned by the U.S. Navy and located in Horsham Township, Montgomery County, Pennsylvania, United States four miles (6 km) northwest of the central business district of Willow Grove, which is north of Philadelphia, Pennsylvania. The installation was transferred to the Pennsylvania Air National Guard and the name changed to the Horsham Air Guard Station after the U.S.