Clarksville is a borough in Greene County, Pennsylvania, United States. The population was 230 at the 2010 census.
Clarksville is located in the northeast corner of Greene County at 39°58′27″N 80°2′41″W (39.974170, -80.044833), at the confluence of Tenmile Creek with its South Fork. The borough is bordered by Morgan Township to the west, by Jefferson Township to the south and east across the South Fork Tenmile Creek, and by East Bethlehem Township in Washington County to the north across Tenmile Creek. Clarksville is 3 miles (5 km) southwest of Millsboro, where Tenmile Creek joins the Monongahela River.
An adjacent part of East Bethlehem Township, Washington County adjacent to the borough is often colloquially considered to be part of Clarksville.
According to the United States Census Bureau, Clarksville has a total area of 0.10 square miles (0.25 km2), all of it land.
As of the census of 2000, there were 234 people, 78 households, and 52 families residing in the borough. The population density was 2,387.1 people per square mile (903.5/km2). There were 90 housing units at an average density of 918.1 per square mile (347.5/km2). The racial makeup of the borough was 96.15% White, 1.28% African American, 0.43% Native American and 2.14% Pacific Islander. Hispanic or Latino of any race were 0.43% of the population.