Horsham is a census-designated place in Horsham Township, Montgomery County, Pennsylvania, United States. The population was 15,193 at the 2020 census. It is home to the Biddle Air National Guard Base at the former site of Naval Air Station Joint Reserve Base Willow Grove. Horsham is coterminous with the ZIP Code 19044. It covers an area of 5.47 miles and is located 16 miles north of Philadelphia.