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. Navy departed in 2011.

Flight activity began in 1926 when Harold Frederick Pitcairn constructed a hangar and a grass airstrip in Horsham, Pennsylvania. The airfield was named after the nearest town Willow Grove, Pennsylvania. At the time, Horsham was a rural township with little significance. From 1926 to 1942 Pitcairn used the airfield for design, construction and testing of a number of aircraft, including the Mailwing which was used by the United States Postal Service.