Williamstown is a town in Orange County, Vermont, United States. The population was 3,515 at the 2020 census, making it the second largest municipality in the county. According to the United States Census Bureau, the town has a total area of 40.3 square miles, of which 40.2 square miles is land and 0.2 square mile is water. The village of Williamstown is in …Williamstown is a town in Orange County, Vermont, United States. The population was 3,515 at the 2020 census, making it the second largest municipality in the county. According to the United States Census Bureau, the town has a total area of 40.3 square miles, of which 40.2 square miles is land and 0.2 square mile is water. The village of Williamstown is in the central part of the town.