Raritan Township is a township in Hunterdon County, New Jersey, United States. As of the 2010 United States Census, the township's population was 22,185, reflecting an increase of 2,376 (+12.0%) from the 19,809 counted in the 2000 Census, which had in turn increased by 4,193 (+26.9%) from the 15,616 counted in the 1990 Census. The township is located within the heart of the Amwell Valley and Raritan Valley regions, as the South Branch of the Raritan River (along with the Neshanic River) flows through the center of the township. The northwestern portion of the township is located on the Hunterdon Plateau.