Hillsborough Township is a township in Somerset County, New Jersey, United States. The township is centrally located in the Raritan Valley region within the much larger New York Metropolitan Area. As of the 2010 United States Census, the township's population was 38,303, reflecting an increase of 1,669 (+4.6%) from the 36,634 counted in the 2000 Census, which had in turn increased by 7,826 (+27.2%) from the 28,808 counted in the 1990 Census.
Hillsborough Township was originally created by Royal charter issued May 31, 1771, which was revoked and revised on September 12, 1771. It was incorporated on February 21, 1798 by the New Jersey Legislature Township Act of 1798 as one of New Jersey's original group of 104 townships. Portions of the township were taken to form the boroughs of Millstone (May 14, 1894) and Manville (April 1, 1929). The township's name may have come from an earlier name of "Hillsbury", though it may have been named for Wills Hill, 1st Marquess of Downshire who was the Earl of Hillsborough.
On May 31, 1771, Hillsborough was officially granted a Charter incorporating it as a Township. A revised charter was issued on September 12, 1771. The records of Hillsborough Township are complete from their inception in 1746 and there are ten volumes, each some several hundred pages, kept in the Special Collections Department of the Rutgers University Library along with the Charter.
Hillsborough Township quickly took its place in history as the path General George Washington and his troops traveled from the Battle of Princeton to winter quarters in Morristown. While the British were encamped in the valley below awaiting an opportunity to attack, it is said that Washington drilled his troops on the Sourland Mountain around a spring near the top using different formations and corn stalks for guns.