The Hargus Lake Trail is a 4 mile loop around the perimeter of Hargus Lake in A.W. Marion State Park near Circleville, Ohio. The trail is well marked with trail signs and blue blazes. Park map is here: http://parks.ohiodnr.gov/Portals/parks/PDFs/parks/Maps/AW_Marion/awmarionparkmap.pdf
The Hargus Lake Trail begins just north of the marina by the boat ramp and follows the perimeter of the lake. It is well marked with trail signs and blue blazes. Travelers beware that there is a separate mountain bike loop (red blazes) that crosses the hiking trail at several points. Once you cross the dam, the trail is briefly broken by a small parking lot. Continue across the parking lot and look for a trail sign on your right along the lakeside.
Note that the CCW loop has a Strava segment, with some times faster than those listed here. FKT aspirants should beat the Strava times.