Greenwich Township () is a township in Warren County, in the U.S. state of New Jersey. As of the 2020 United States census, the township's population was 5,473,
Greenwich Township has at various times been a part of most of Northwestern New Jersey's counties. The township was first mentioned in official documents on October 9, 1738, as a part of Hunterdon County. On March 15, 1739, it became part of the newly formed Morris County. On January 22, 1750, portions of the township were taken to form Hardwick Township. On June 8, 1753, Sussex County was created, and Greenwich Township was shifted again. Portions of the township were taken on May 30, 1754, to form both Mansfield Township and Oxford Township. The township was incorporated by an act of the New Jersey Legislature on February 21, 1798. It found its current home when Warren County was formed on November 20, 1824. On April 8, 1839, portions of the township were taken to create Franklin Township and Harmony Township. On March 7, 1851, Phillipsburg was created from parts of Greenwich, and Pohatcong Township went off on its own as of January 1, 1882. The township was named for Greenwich, England.
Geography
According to the U.S. Census Bureau, the township had a total area of 10.60 square miles (27.45 km<sup>2</sup>), including 10.58 square miles (27.40 km<sup>2</sup>) of land and 0.02 square miles (0.04 km<sup>2</sup>) of water (0.15%).
Other unincorporated communities, localities and place names located partially or completely within the township include Coopersville, Kennedy Mills, Port Warren and Still Valley.
Greenwich Township borders the municipalities of Franklin Township, Lopatcong Township and Pohatcong Township in Warren County; and Bloomsbury in Hunterdon County.