Charlestown is a town in Sullivan County, New Hampshire, United States. The population was 5,114 at the 2010 census. The town is home to Hubbard State Forest and the headquarters of the Student Conservation Association.
The primary settlement in town, where 1,152 people resided at the 2010 census, is defined as the Charlestown census-designated place (CDP) and is located along New Hampshire Route 12. The town also includes the villages of North Charlestown, South Charlestown and Hemlock Center.
The area was first granted in 1735 by Colonial Governor Jonathan Belcher of Massachusetts as Plantation No. 4, the fourth in a line of forts on the Connecticut River border established as trading posts. Settled in 1740, Number Four was the northernmost township, and its 1744 log fort became a strategic military site throughout the French and Indian Wars. Several settlers were ambushed and captured by the Indians, and in 1747 the fort was besieged for three days by a force of 400 French and Indians. Captain Phineas Stevens and 31 soldiers, stationed at the fort, repelled the attack. Their success became well-known, and the fort was never attacked again.