Langdon is a town in Sullivan County, New Hampshire, United States.

Built across Great Brook in 1874, the lattice truss span has a length of 34 feet 6 inches (10.52 m).

According to the United States Census Bureau, the town has a total area of 16.3 square miles (42.3 km2), of which 0.1 square miles (0.2 km2) are water, comprising 0.45% of the town.

[4] The highest point in town is the summit of Holden Hill, at 1,348 feet (411 m) above sea level.

21.1% of all households were made up of individuals, and 8.4% had someone living alone who was 65 years of age or older.