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 (+17.8%) from the 8,970 counted in the 2000 Census, which had in turn increased by 3,901 (+77.0%) 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 (now Roosevelt). The township was named for the Millstone River, whose name derives from an incident in which a millstone was dropped into it.
The township has been one of the state's highest-income communities. Based on data from the American Community Survey for 2013–2017, Millstone Township residents had a median household income of $156,891, ranked 9th in the state among municipalities with more than 10,000 residents, more than double the statewide median of $76,475.
According to the United States Census Bureau, the township had a total area of 37.18 square miles (96.30 km2), including 36.61 square miles (94.81 km2) of land and 0.58 square miles (1.49 km2) of water (1.55%).
There are two unincorporated communities within the township served by the United States Postal Service as post offices. Clarksburg is served by post office ZIP Code 08510 and Perrineville is served as ZIP code 08535. Other unincorporated communities and place names located entirely or partially within the township include Baird, Bairdsville, Bergen Mills, Burksville, Carrs Corner, Carrs Tavern, Charleston Springs, Disbrow Hill, Ely, Elys Corner, Fair Play, Hillhurt, Holmeson, Pine Hill, Smithburg, Stone Tavern and Sweetman.
The township borders Freehold Township, Manalapan Township, Roosevelt and Upper Freehold Township in Monmouth County; East Windsor Township and Robbinsville Township in Mercer County; Monroe Township in Middlesex County; and Jackson Township in Ocean County.
According to the A. W. Kuchler U.S. potential natural vegetation types, Millstone Township, New Jersey would have an Appalachian Oak (104) vegetation type with an Eastern Hardwood Forest (25) vegetation form.
The 2010 United States Census counted 10,566 people, 3,301 households, and 2,888 families in the township. The population density was 288.8 inhabitants per square mile (111.5/km2).