Mount Holly is a township that is the county seat of Burlington County in the U.S. state of New Jersey. It is an eastern suburb of Philadelphia, the nation's sixth largest city as of 2020. As of the 2020 United States census, the township's population was 9,981, an increase of 445 (+4.7%) from the 2010 census count of 9,536, which in turn reflected a decline of 1,192 (-11.1%) from the 10,728 counted in the 2000 census. The township, and all of Burlington County, is a part of the Philadelphia metropolitan area.