Thornton is a town in Grafton County, New Hampshire, United States. The population was 2,490 at the 2010 census.
Thornton was incorporated in 1763, and named for Doctor Matthew Thornton, a signer of the Declaration of Independence.
According to the United States Census Bureau, the town has a total area of 50.8 square miles (131.6 km2), of which 50.2 square miles (130.0 km2) is land and 0.6 square miles (1.6 km2) is water, comprising 1.19% of the town. The highest point in Thornton is 2,580 feet (790 m) above sea level on the western ridge of Dickey Mountain, whose 2,734-foot (833 m) summit lies in the neighboring town of Waterville Valley.
At the 2000 census there were 1,843 people, 759 households, and 507 families living in the town. The population density was 36.6 people per square mile (14.1/km²). There were 1,487 housing units at an average density of 29.5 per square mile (11.4/km²). The racial makeup of the town was 97.61% White, 0.27% African American, 0.11% Native American, 0.27% Asian, 0.05% Pacific Islander, 0.33% from other races, and 1.36% from two or more races. Hispanic or Latino of any race were 0.71%.
Of the 759 households 29.6% had children under the age of 18 living with them, 56.5% were married couples living together, 6.6% had a female householder with no husband present, and 33.2% were non-families. 21.1% of households were one person and 6.6% were one person aged 65 or older. The average household size was 2.43 and the average family size was 2.86.