Sparta is a township in Sussex County in the U.S. state of New Jersey. As of the 2020 United States census, the township's population was 19,600, a decrease of 122 (−0.6%) from the 2010 census count of 19,722, which in turn reflected an increase of 1,642 (+9.1%) from the 18,080 counted in the 2000 census.