Sparta Township is a township in Sussex County, New Jersey, United States. As of the 2010 United States Census, the township's population was 19,722, reflecting an increase of 1,642 (+9.1%) from the 18,080 counted in the 2000 Census, which had in turn increased by 2,923 (+19.3%) from the 15,157 counted in the 1990 Census.