Williamstown is an unincorporated community and census-designated place[9] (CDP) located in Monroe Township in Gloucester County, in the U.S. state of New Jersey.

[14] Before the community's settlement in 1737, Williamstown was inhabited by the Lenni-Lenape tribe of Native Americans, from whom the town derived its original name, "Squankum", for "place where evil spirits dwell".

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.

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 company to form was called Free Will Glass Manufacturing and caused a population surge.

One notable company, The John Sharp Canning Co., still operates today as Blue Ribbon.

The Monroe Township Historical Society was formed as a volunteer organization on October 16, 1974, by Mayor John W. Sharp (of the Canning Company Sharps), dedicated to the preservation of items that reflect the history of Monroe Township.

In 2014, the community had a death rate from heroin that was 25 times the national average, with about five people per year dying of overdoses and other complications in the previous decade.

[5][19] It has a humid subtropical climate (Cfa) and average monthly temperatures range from 33.2° in January to 76.7 °F in July.

The 2010 United States census counted 15,567 people, 5,592 households, and 4,037 families in the CDP.

[25] Operating since 1961 and located within five minutes from the center of Williamstown, Hospitality Creek is a campground consisting of an RV park, Olympic-size swimming pool, 30-acre (12 ha) lake, and other outdoor amenities.