Hillsborough Township is a township in Somerset County, New Jersey, United States. As of the 2010 United States Census, the township's population was 38,303, reflecting an increase of 1,669 from the 36,634 counted in the 2000 Census, which had in turn increased by 7,826 from the 28,808 counted in the 1990 Census.Hillsborough Township was originally created by Royal charter on September 12, 1771, from portions of Western precinct. It was incorporated by an act of the New Jersey Legislature on February 21, 1798, as one of New Jersey's original group of 104 townships. Portions of the township were taken to form the boroughs of Millstone and Manville. 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.