Cassville is a borough in Huntingdon County, Pennsylvania, in the United States. As of the 2010 census, the borough population was 143.Cassville is located in south-central Huntingdon County at 40°17′35″N 78°1′40″W / 40.29306°N 78.02778°W / 40.29306; -78.02778, at an elevation of 1,241 feet. It sits at the western base of Sideling Hill, which rises 400 feet above the borough. Shirley Knob rises 600 feet above the borough to the southwest.Pennsylvania Route 829 passes through the center of Cassville, leading north 12 miles to U.S. Route 22 near Mill Creek and south over Sideling Hill 7 miles to Saltillo.According to the United States Census Bureau, Cassville has a total area of 0.6 square miles, all of it land.As of the census of 2000, there were 152 people, 65 households, and 46 families residing in the borough. The population density was 266.6 people per square mile. There were 69 housing units at an average density of 121.0 per square mile.