Its eastern terminus is at U.S. Route 59 in Mound City; its western terminus is at Route 111 about six miles (10 km) west of Mound City.

The route heads through agricultural areas with some trees, intersecting Route P. The road passes through the community of Bigelow, where it crosses BNSF Railway's Napier Subdivision.

Past Bigelow, Route 118 curves northeast and passes Loess Bluffs National Wildlife Refuge on its south.

The road reaches Mound City, where it comes to an interchange with I-29.

A short distance later, Route 118 comes to its eastern terminus at US 59.