Union Township is a township in Hunterdon County, in the U.S. state of New Jersey. The southwest half of the township lies on what is known as the Hunterdon Plateau, the northwest corner consists of the Musconetcong Ridge and the northeast section is part of the lower-lying Newark Basin around Spruce Run Reservoir. As of the 2020 United States census, the township's population was 6,507, its highest ever decennial count and an increase of 599 (+10.1%) from the 2010 census count of 5,908, which in turn reflected a decline of 252 (−4.1%) from the 6,160 counted in the 2000 census.

Pittstown is an unincorporated community located at the intersection of the boundaries of Alexandria, Franklin and Union townships in Hunterdon County, New Jersey. The area is named after William Pitt. The area is served as United States Postal Service ZIP Code 08867. The area was named Hofftown in the 18th century after landowner Lawrence Hoff. The Pittstown Historic District was listed on the state and national registers of historic places in 1990.