National Park Service Route 615 begins at the Warren and Sussex County line south of Flatbrookville, New Jersey.

The route soon enters the small community of Flatbrookville, New Jersey (now maintained by the National Park Service), winding through woodlands as a two-lane asphalt highway.

The highway continues down the Flat Brook Valley, passing a local RV park before heading northbound through woodlands, where it curves to the north.

At the intersection with Bridge Road, National Park Service Route 615 turns to the north and heads through forestry before passing nearby houses.

The highway continue northeastward through Peters Valley, a small art-based community before heading northward through the local police archery and reaching the site of a trail, where Route 615 turns to the east.

[1] However, until 2009, signage continued along Ennis Road, a two concrete lane, closed off portion of Route 615 through the ruralmost parts of Sandyston Township.

[5] The alignment continued to the southeast, crossing through farmland until entering forestry, where it bended several times until reaching a concrete parking lot.