Branchburg is a township in Somerset County, New Jersey, United States. As of the 2010 United States Census, the township's population was 14,459, reflecting a decline of 107 (−0.7%) from the 14,566 counted in the 2000 Census, which had in turn increased by 3,678 (+33.8%) from the 10,888 counted in the 1990 Census.
While the area of today's Branchburg has a history antedating the American Revolutionary War, the township itself was incorporated by an act of the New Jersey Legislature on April 5, 1845, from portions of Bridgewater Township. The township is named for its location at a point where branches of the Raritan River merge.
The land that is now known as Branchburg Township was originally inhabited by the Raritans, a tribe of the Lenni Lenape Native Americans. By 1686 most of the land was purchased from the Lenape by the Lords Proprietors of East Jersey, who sold the land in small parcels to numerous settlers, mostly of Dutch or English extraction. With the 1688 redrawing of the boundary between East and West Jersey, the Branchburg region was split between Essex County to the north and the newly formed Somerset County to the south. With Somerset's acquisition of territory from Essex and Middlesex Counties in 1741, Branchburg lay entirely within Somerset County.
Bridgewater Township was chartered in 1749. The residents of the part of Bridgewater west of the Raritan River petitioned the New Jersey Legislature for incorporation as a separate township, which was granted by an act dated April 5, 1845. The first town meeting was held April 14, 1845, in White Oak Tavern, a stagecoach stop and local meeting place along the Old York Road.
According to the United States Census Bureau, the township had a total area of 20.279 square miles (52.521 km2), including 20.044 square miles (51.912 km2) of land and 0.235 square miles (0.609 km2) of water (1.16%).
The township is 11 miles (18 km) long and approximately 2 miles (3.2 km) across at its widest point. Unincorporated communities, localities and place names located partially or completely within the township include Burnt Mill, Centerville, Fox Hollow, Neshanic, Neshanic Station (ZIP Code 08853) and North Branch (ZIP Code 08876), North Branch Depot and Woodfern.
The township is bordered on the west by Readington Township in Hunterdon County; on the north by Bedminster Township and on the south by Bridgewater Township and Hillsborough Township.
The main watercourses are the Lamington River on the north, the North Branch of the Raritan River on the east and the South Branch of the Raritan River on the east and south. These rivers along with small streams and brooks are excellent for fishermen who enjoy trout stocked streams and rivers.