West Windsor Township is a township in Mercer County, New Jersey, in the United States. As of the 2010 United States Census, the township's population was 27,165, reflecting an increase of 5,258 (+24.0%) from the 21,907 counted in the 2000 Census, which had in turn increased by 5,886 (+36.7%) from the 16,021 counted in the 1990 Census.West Windsor Township was established by an act of the New Jersey Legislature on February 9, 1797, and incorporated on February 21, 1798, as one of the state's initial group of 104 townships. The Borough of Princeton (now part of Princeton) was formed from portions of the township on February 11, 1813. The township is closely associated with that now much more widely known town and several localities within West Windsor use Princeton in their name, the most notable of those being Princeton Junction. The USPS 'Princeton' post office (08540) facility is located within West Windsor, and covers parts of the township designated by Princeton, NJ mailing addresses.A portion of Princeton University covering south of Lake Carnegie is located in West Windsor Township. The University agreed in 2009 to make an annual payment in lieu of taxes of $50,000 that would be indexed to inflation to cover of land in the township that the university had purchased in 2002.