Williamstown is a borough in Dauphin County, Pennsylvania, United States.

Formerly, anthracite coal mines and hosiery mills were located in the borough.

According to the United States Census Bureau, the borough has a total area of 0.26 square miles (0.67 km2), all land.

There were 716 housing units at an average density of 2,844.1 per square mile (1,098.1/km2).

29.0% of all households consisted of individuals, and 15.9% were single residents 65 years of age or older.