It runs from near the town center of Equality at Calhoun Street, a local road, north to Illinois Route 37 and the northern terminus of Illinois Route 148 in Mount Vernon.

Vernon, Illinois 142 passes the sole remaining Continental Tire North America manufacturing plant, becoming Fisher Lane for a short distance before intersecting IL 37.

It proceeds along Veterans Memorial Drive ending at the northern terminus of Illinois Route 148 (Waltonville Road).

This configuration lasted until 1974, when U.S. 460 was decommissioned and the current routing for Illinois 142 re-established from Mount Vernon to McLeansboro.

[2] Illinois Route 142 runs roughly parallels to and near the path of the historic Goshen Road in the counties it traverses.