is a borough in Franklin County, Pennsylvania, 73 miles (117 km) southwest of Harrisburg. Originally called Black Town, it was incorporated in 1831. In 1900, 956 people lived here, and in 1910, 1,410 people lived here. The population was 1,540 at the 2000 census.
According to the United States Census Bureau, the borough has a total area of 1.0 square miles (2.5 km²), all of it land.
Mercersburg is located at the foot of the Appalachian mountains just north of the Mason-Dixon Line, which serves as the state border with Maryland. Whitetail Ski Resort is located near the town, open all winter long
Pennsylvania state highways 16, 75 and 416 all pass through Mercersburg, which is approximately 10 miles west of Interstate 81.