Clark is a borough in Mercer County, Pennsylvania, United States. The population was 633 at the 2000 census. It is part of the Youngstown–Warren–Boardman, OH-PA Metropolitan Statistical Area.
Clark is located at 41°16′55″N 80°24′35″W / 41.28194°N 80.40972°W / 41.28194; -80.40972 (41.282049, -80.409591).
According to the United States Census Bureau, the borough has a total area of 3.8 square miles (9.8 km²), of which, 3.0 square miles (7.9 km²) of it is land and 0.7 square miles (1.9 km²) of it (19.31%) is water.