Cassville is a borough in Huntingdon County, Pennsylvania, United States.

It sits at the western base of Sideling Hill, which rises 400 feet (120 m) above the borough.

Pennsylvania Route 829 passes through the center of Cassville, leading north 12 miles (19 km) to U.S. Route 22, near Mill Creek and south over Sideling Hill 7 miles (11 km) to Saltillo.

According to the United States Census Bureau, Cassville has a total area of 0.6 square miles (1.6 km2), all land.

About 11.4% of families and 9.9% of the population were below the poverty line, including none of those under the age of eighteen and 12.5% of those sixty five or over.