Marlboro Township is a township in Monmouth County, New Jersey, United States. As of the 2010 United States Census, the township had a population of 40,191, reflecting an increase of 5,449 from the 33,423 counted in the 2000 Census, which had in turn increased by 6,707 from the 26,716 counted in the 1990 Census.Marlboro Township was formed by an act of the New Jersey Legislature on February 17, 1848, from portions of Freehold Township. The township was named for the marl beds found in the area.