

The township borders the Hunterdon County municipalities of Alexandria Township, Bethlehem Township, Clinton, Clinton Township, Franklin Township and Lebanon Township. Pittstown is an unincorporated community that is also spread across Alexandria Township and Franklin Township. Unincorporated communities, localities and place names located partially or completely within the township include Coles Mills, Grandin, Hensfoot, Jutland, Kingtown, Mechlings Corner, Mount Salem, Norton, Pattenburg, Perryville, Polktown and Van Syckel. Geography Īccording to the United States Census Bureau, township had a total area of 20.63 square miles (53.43 km 2), including 18.77 square miles (48.60 km 2) of land and 1.86 square miles (4.83 km 2) of water (9.03%). New Jersey Monthly magazine ranked Union Township 21st in its 2008 rankings of the "Best Places To Live" in New Jersey.

A farm community developed, together with basket making and tanning industries. Farms and fields were established in areas where trees were felled to provide fuel for the furnace. Union Furnace and its forge produced cannonballs for the Revolutionary War and shoes for horses and oxen, as well as farm implements.

The name "Union" was chosen over the alternative "Rockhill", which was a community at the southern end of the township. The township was named for Union Furnace, which was producing iron from 1742 until the 1780s. Clinton Town was formed on April 5, 1865, within portions of the township, and became an independent municipality in 1895. Union was incorporated as a township by an act of the New Jersey Legislature on February 17, 1853, from portions of Bethlehem Township. 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. 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. Union Township is a township in Hunterdon County, in the U.S.
