Marietta is a borough in Lancaster County, Pennsylvania, United States. The population was 2,689 at the 2000 census. It is located on the east bank of the Susquehanna River just north of Columbia.
Marietta is located at 40°3′26″N 76°33′21″W / 40.05722°N 76.55583°W / 40.05722; -76.55583 (40.057169, -76.555955).
According to the United States Census Bureau, the borough has a total area of 0.8 square miles (1.9 km²), all of it land.