The trail runs for 45 miles from Feazel Street in Harrisburg to Karmak in southern Illinois. The trail is managed by Illinois Department of Natural Resources. From Karnak, a 2.5 mile spur on the old Chicago and Eastern Illinois Railroad runs to the new Henry Barkhausen Wetlands Center.
The Tunnel Hill Trail is part of a former railroad founded by Civil War General Ambrose Burnside. In 1872 Burnside and others began the Vincennes & Cairo Railroad, which connected Vincennes, Indiana and Cariro, Illinois. The railroad changed hands through the years and was operated as the Wabash, St. Louis & Pacific; the New York Central; Penn Central; Conrail; and during its most productive years, the Cleveland, Chicago, Cincinnati & St. Louis Railroad, known as the Big Four. The last owners were the Southern Railway and following a merger, the Norfolk Southern Railroad.
Beginning in Harrisburg, the trail is at 370 feet above sea level, rising to 680 feet at Tunnel Hill and then dropping to 340 feet at Karnak. A 543-foot long tunnel gave the nearby town its name, and now the trail. The trail crosses 23 trestles ranging from 34 feet long to 450 feet. The longest, Breeden Trestle, is also the highest at 90 feet. The abandoned railroad right-of-way varies between 40 and 200 feet in width.
The Tunnel Hill State Trail connects a number of communities, hamlets, and ghost towns. It is a day-use facility, offering drinking water, privy toilets, and parking in access areas. Several campgrounds are located nearby. The site office is in Vienna, and includes interpretive displays and other information.
