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.
Source: Snyder, John P. The Story of New Jersey's Civil Boundaries: 1606-1968, Bureau of Geology and Topography; Trenton, New Jersey; 1969. p. 182.