Willow Grove is a census-designated place (CDP) in Montgomery County, Pennsylvania, about 10 miles north of Philadelphia. The population was 16,234 at the 2000 census. Willow Grove was once known for Willow Grove Park, an amusement park that was open from 1896 to 1976, now the site of Willow Grove Park Mall. Naval Air Station Joint Reserve Base Willow Grove is located northwest of the Willow Grove CDP in Horsham Township. NAS JRB Willow Grove will continue operating through 2010, and closure will occur by September 2011.