Hillsborough Township was originally created by Royal charter issued May 31, 1771, which was revoked and revised on September 12, 1771.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.