The southern terminus of the highway is at the Florida state line, where it serves as a continuation of State Road 77 (SR 77).

The northern terminus of the highway is at an intersection with U.S. Route 231 (US 231) north of Madrid.

SR 109 is routed along a two-lane road for its entire length.

It serves as a connecting route between Graceville, Florida and Dothan, Alabama.

Graceville is located approximately 5 miles (8.0 km) south of the Florida state line.