Beattystown is an unincorporated community and census-designated place located within Mansfield Township, in Warren County, in the U.S. state of New Jersey. As of the 2010 United States Census, the CDP's population was 4,554. Beattystown has been listed as one of the 10 most endangered historic sites in New Jersey by Preservation New Jersey. Beattystown was named after George Beatty, who built a mill here c. 1762.