Running for about 60 miles (97 km) in a general east–west direction, connecting rural portions of Elkhart, LaGrange and Steuben counties.

The western terminus is a junction with Jackson Boulevard and Middleton Run Road in Elkhart.

The modern route of SR 120 was originally just small part of a much longer Native American trail.

In the early 1920s a project to construct a road replacing the Native American trail took place.

It follows Jackson Boulevard, northeasterly paralleling the St. Joseph River and the Grand Elk Railroad.

In LaGrange county the road enters the town of Howe, passing through an intersection with SR 9.

[13] The following year Steuben County was having trouble maintaining the roadway, with bridges needing replacement and the gravel road surface was deteriorating.

The western end of SR 120 was moved once again to an intersection between Jackson Boulevard and Middleton Run Road on September 9, 2000.