Manalapan Township is a township in Monmouth County, New Jersey, United States. As of the 2010 United States Census, the township's population was 38,872, representing an increase of 5,449 (+16.3%) from the 33,423 counted in the 2000 Census, which had in turn increased by 6,707 (+25.1%) from the 26,716 counted in the 1990 Census.