The Darlington Trail's western terminus begins at the junction of the Appalachian and Tuscarora Trails within Pennsylvania State Game Lands 170. It ends at the eastern terminus at Tower Road, some 7.73 miles away. The trail is maintained by volunteers from the Susquehanna Appalachian Trail Club based in the capital city of Harrisburg.
The trail varies from highly runnable single track to technical rocky sections to wooded forest roads. There are two proper road crossings though only one of those two roads is paved. There is one small stream crossing in the area of Bryson Hollow near the eastern terminus. At least 5 miles of the route mostly follows the top of the ridge before descending in to the Bryson Hollow area.
The western terminus sees high foot traffic due to its intersection with two other established trails but the eastern terminus is much more remote since it dead ends at a forest road that sees little vehicle traffic.
While there are websites that suggest this route ranges from 7.75 miles all the way up to 18+ miles, my Garmin watch calculated 7.73 miles. The 18 mile reference harkens back to years ago when the trail continued past Tower Road and crossed the Susquehanna River. It's since been shortened.