Williamstown is an unincorporated community and census-designated place (CDP) located within Monroe Township, in Gloucester County, New Jersey, United States. As of the 2010 United States Census, the CDP's population was 15,567.
Before settlement in 1737, Williamstown was inhabited by the Lenni-Lenape tribe of Native Americans, from whom the town derived its original name, "Squankum." The name (Lenape for 'place where evil spirits dwell') was changed to Williamstown when the town's first post office was established, due to postal regulations that prohibited two towns from having the same name and there was an older Squankum located 60 miles (97 km) northeast. It is generally thought that 'evil spirits' referred to the abundance of mosquitoes in the area, a by-product of the low-lying swamps that characterized the area during that time period. In the early eighteenth century, Richard Penn sold what eventually became Williamstown to his grandson, John Williams, who divided and resold the land in lots to settlers and for whom the town was eventually renamed. The town was officially incorporated as Monroe Township in March 1859, with Williamstown as meeting place to vote and have town discussions. A municipal court was established in the Township of Monroe, in accordance with the provisions of Chapter 264 of the Laws of 1948. The first school was built in 1750 and stood where the Washington Hotel now stands. The local schools operated on a pay-as-you-go basis until the 1850s and were predominantly church-run. The area built its first high school in 1958.
The population of the town remained small until the early 1830s when the glass industry sprung up (Glassboro, a neighboring town, still bears the name borne of that commercial boom).