This branch headed west from the Pennsylvania Railroad's main line that ran between Harrisburg, PA, and Hagerstown, MD, via Chambersburg, PA. It branched from the main near Marion, and passed through the communities of Stonebridge, Williamson, McCulloch, Lemasters, Mercersburg Junction, and terminated at Mercersburg. It appears to have been abandoned in the 1970s. At Mercersburg Junction, a 5-mile branch that had been abandoned even earlier headed north through Gap Road, Creigh, Fort Loudon and terminated at Richmond.

The right of way passed through rural farms and other open areas. The right of way is now largely obscured, and much of it is inaccessible on private property.

The site called Mercersburg Junction (there is no town there) is near PA Route 416, just south of where the highway crosses over the West Branch of the Conococheague Creek. The former branch to Richmond is used as a farm access road in this area.