Manalapan Township is a township in western Monmouth County, in the U.S. state of New Jersey. The township is centrally located within the Raritan Valley region and is a part of the New York metropolitan area. As of the 2020 United States census, the township's population was 40,905, its highest decennial count ever and an increase of 2,033 from the 20…Manalapan Township is a township in western Monmouth County, in the U.S. state of New Jersey. The township is centrally located within the Raritan Valley region and is a part of the New York metropolitan area. As of the 2020 United States census, the township's population was 40,905, its highest decennial count ever and an increase of 2,033 from the 2010 census count of 38,872, which in turn reflected an increase of 5,449 from the 33,423 counted in the 2000 census.