Dorchester is a town in Grafton County, New Hampshire, United States. The population was 355 at the 2010 census.
According to the United States Census Bureau, the town has a total area of 45.2 square miles (117 km), of which 44.7 sq mi (116 km) is land and 0.6 sq mi (1.6 km) is water, comprising 1.22% of the town. It is drained by the South Branch Baker River and Indian River. The highest point in Dorchester is on its western boundary, where the elevation reaches 3,190 feet (970 m) above sea level, just east of the summit of Smarts Mountain. Dorchester lies within two watersheds — roughly the southwestern half of town is in the Connecticut River watershed and the northeastern half is in the Merrimack River watershed.
The town is crossed by New Hampshire Route 118.
As of the census of 2000, there were 353 people, 132 households, and 99 families residing in the town. The population density was 7.9 people per square mile (3.0/km²). There were 236 housing units at an average density of 5.3 per square mile (2.0/km²). The racial makeup of the town was 97.17% White, 0.28% African American, 0.28% Native American, 0.85% Asian, 0.85% from other races, and 0.57% from two or more races. Hispanic or Latino of any race were 0.57% of the population.
There were 132 households out of which 35.6% had children under the age of 18 living with them, 59.8% were married couples living together, 9.8% had a female householder with no husband present, and 25.0% were non-families. 19.7% of all households were made up of individuals and 6.1% had someone living alone who was 65 years of age or older. The average household size was 2.67 and the average family size was 3.02.
In the town, the population was spread out with 27.5% under the age of 18, 5.4% from 18 to 24, 26.3% from 25 to 44, 28.9% from 45 to 64, and 11.9% who were 65 years of age or older. The median age was 40 years. For every 100 females, there were 98.3 males. For every 100 females age 18 and over, there were 95.4 males.
The median income for a household in the town was $40,833, and the median income for a family was $42,292. Males had a median income of $35,000 versus $24,375 for females. The per capita income for the town was $18,940. About 8.6% of families and 11.3% of the population were below the poverty line, including 17.2% of those under age 18 and 9.5% of those age 65 or over.