See also: Williamstown (CDP), Massachusetts
As of the census of 2000, there were 8,424 people, 2,753 households, and 1,693 families residing in the town. Williamstown is the fourth-largest town in Berkshire County, and ranks 189th out of the 351 cities and towns in Massachusetts by population. The population density was 179.7 people per square mile (69.4/km²), ranking it 7th in the county and 264th in the Commonwealth. There were 3,053 housing units at an average density of 65.1/sq mi (25.1/km²). The racial makeup of the town was 90.79% White, 2.72% Black or African American, 0.11% Native American, 3.12% Asian, 0.12% Pacific Islander, 0.77% from other races, and 2.37% from two or more races. Hispanic or Latino of any race were 2.77% of the population.
There were 2,753 households out of which 24.7% had children under the age of 18 living with them, 51.3% were married couples living together, 7.9% had a female householder with no husband present, and 38.5% were non-families. 32.7% of all households were made up of individuals and 15.7% had someone living alone who was 65 years of age or older. The average household size was 2.21 and the average family size was 2.80.
In the town the population was spread out with 15.3% under the age of 18, 27.5% from 18 to 24, 16.6% from 25 to 44, 21.0% from 45 to 64, and 19.6% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 87.8 males. For every 100 females age 18 and over, there were 85.8 males.
The median income for a household in the town was $51,875, and the median income for a family was $67,589. Males had a median income of $50,011 versus $32,845 for females. The per capita income for the town was $26,039. About 1.7% of families and 5.5% of the population were below the poverty line, including 1.3% of those under age 18 and 6.8% of those age 65 or over.