Mid State Trail (Pennsylvania)

The Mid State Trail (MST) is a 526-kilometre (327 mi) linear hiking trail located in the Appalachian Mountains and Allegheny Plateau of central Pennsylvania, United States. It is the longest hiking trail in Pennsylvania, and one of just three (with the Appalachian Trail and North Country Trail) to traverse the state from one border to another. A portion of the Mid State Trail is also part of the Great Eastern Trail.

The Mid State Trail is known for its feeling of remoteness, though it is never more than 2 kilometres (1.2 mi) from a road. It is mostly on public lands, including state forest and state game lands, and it passes through numerous state parks, wild areas, and natural areas. In its southern half, the MST mostly follows rocky ridgetops in the ridge and valley province and reaches dozens of expansive vistas. The northern segment of the trail traverses slightly less rugged but still challenging landscapes on top of the Allegheny Plateau.

The original route of the trail extended from near Alexandria on US Route 22 in Huntingdon County, to the West Rim Trail near Blackwell in Tioga County. It has since been extended to both the south and north, reaching from Maryland to New York and connecting with other trails in those states.

The MST is marked by orange blazes, with some spur trails to nearby points of interest marked by blue blazes. The MST holds the distinction of being measured entirely in metric, with all guidebooks and signs using metric distances while maps also show metric elevations. It was the first significant hiking trail in the United States to do so. This is because the founder of the trail, Tom Thwaites, was a proponent of converting America to the metric system.