Stillwater Township is a township located in Sussex County, New Jersey, United States. Located in the Kittatinny Valley, Stillwater is a rural farming community with a long history of dairy farming. As of the 2010 United States Census, the township's population was 4,099, reflecting a decrease of 168 (−3.9%) from the 4,267 counted in the 2000 Census, which had in turn increased by 14 (+0.3%) from the 4,253 counted in the 1990 Census. In 2008, New Jersey Monthly magazine ranked Stillwater Township as its 40th best place to live in its annual rankings of the "Best Places To Live" in New Jersey.