Green Brook Township is a township in Somerset County, in the U.S. state of New Jersey. It is centrally located within the Raritan Valley region. As of the 2020 United States census, the township's population was 7,281,
What is now Green Brook was originally created as North Plainfield Township on April 2, 1872, from portions of Warren Township. Portions of the township were taken to form North Plainfield (June 9, 1885) and Watchung (March 23, 1926). Green Brook was incorporated as a township by an act of the New Jersey Legislature on November 8, 1932, replacing North Plainfield Township, based on the results of a referendum held that same day.
Green Brook describes itself as "Small Enough to Know You, Large Enough to Get Things Done". The brook was named for the color of its water.
Also contained within the township is Washington Rock State Park, which commemorates the spot where George Washington and Marquis de Lafayette watched the movement of the British soldiers during the American Revolutionary War, mainly the months of May and June 1777. The park was established on March 17, 1913, and is about in size.
Raritan Valley Hospital in Green Brook was the first teaching hospital of Rutgers Medical School when in 1972 the school expanded to become a full four-year medical school. The hospital had opened in 1966 and was closed in 1981, with the subsequent conversion to the Green Brook Regional Center, a facility caring for the elderly with disabilities.
Geography
According to the United States Census Bureau, the township had a total area of 4.42 square miles (11.43 km<sup>2</sup>), including 4.41 square miles (11.42 km<sup>2</sup>) of land and 0.01 square miles (0.02 km<sup>2</sup>) of water (0.18%).
Unincorporated communities, localities and place names located partially or completely within the township include Seeley Mills and Washington Rock.
The township borders the municipalities of Bridgewater Township, North Plainfield, Warren Township and Watchung in Somerset County; Middlesex and Dunellen in Middlesex County; and Plainfield in Union County.