Charlestown is a town in Sullivan County, New Hampshire, United States. The population was 4,749 at the 2000 census. Charlestown includes the villages of North Charlestown, South Charlestown and Hemlock Center. The town is home to Hubbard State Forest and the headquarters of the Student Conservation Association. The primary settlement in town, where 24% of the population resides, is defined by the U.S. Census Bureau as the Charlestown census-designated place (CDP) and is located along New Hampshire Route 12.