Gilsum is a town in Cheshire County, New Hampshire, United States. The population was 813 at the 2010 census. Home to the Bear's Den Natural Area, Gilsum includes Gilsum Lower Village.
The land was originally named Boyle after Richard Boyle, Earl of Burlington, when the land was granted by the Masonian Proprietors in 1752, but ongoing hostilities during the French and Indian War prevented settlement. When the grant lapsed, the town was rechartered by Governor Benning Wentworth on July 13, 1763 as Gilsum, combining the surnames of two proprietors, Samuel Gilbert and his son-in-law, Thomas Sumner. It was first settled in 1764 by Josiah Kilburn from Hebron, Connecticut.
The Ashuelot River provided water power for woolen mills. By 1859, when the population was 668, there was also a bobbin factory, a chair factory, and a tannery. Gilsum used to be a center for mining mica and feldspar. High-quality crystals, especially beryl, tourmaline, and quartz, can also be found. Today, Gilsum is headquarters to the W.S. Badger Company, makers of "balms, potions and natural remedies."
The town contains the Stone Arch Bridge, completed in 1863 with the highest vault (36 feet, 6 inches) of any mortarless bridge in New Hampshire.