Millstone Township is a township in Monmouth County, New Jersey, United States. It is located in the New York Metropolitan Area. As of the 2010 United States Census, the township's population was 10,566, reflecting an increase of 1,596 from the 8,970 counted in the 2000 Census, which had in turn increased by 3,901 from the 5,069 counted in the 1990 Census.Millstone was formed as a township by an act of the New Jersey Legislature on February 28, 1844, from portions of Freehold Township and Upper Freehold Township, as well as part of Monroe Township in Middlesex County. The portions taken from Monroe Township were relinquished in 1845. On May 29, 1937, portions of the township were taken to form the borough of Jersey Homesteads. The township was named for the Millstone River, whose name derives from an incident in which a millstone was dropped into it.