Williamstown is a home-rule-class city in Grant and Pendleton counties in the U.S. state of Kentucky.

The Cincinnati Southern Railway was built through the county in 1877, and Williamstown Lake was created in 1957.

Interstate 75 passes through the west side of the city, with access from Exits 154 and 156.

U.S. Route 25 passes through the center of Williamstown as Main Street; US 25 leads north 11 miles (18 km) to Crittenden and south the same distance to Corinth.

[5] Williamstown Lake, a reservoir on the South Fork of Grassy Creek, is in the northeast part of the city.

The climate in this area is characterized by hot, humid summers and generally mild to cool winters.

28.4% of all households were made up of individuals, and 15.9% had someone living alone who was 65 years of age or older.