Dunellen is a borough in Middlesex County, in the U.S. state of New Jersey. It is located within the Raritan Valley region of central New Jersey. As of the 2020 United States census, the borough's population was 7,637, an increase of 410 from the 2010 census count of 7,227, which in turn had reflected an increase of 404 from the 6,823 counted at the 2000 census.