It runs through southern Choctaw County, connecting to US-70 at each end.

The highway begins heading southbound from US-70 at Boswell.

As it approaches the Red River, it turns back northward and then eastward again to run through unincorporated Gay, 24 miles[2] (38.6 km) into the route.

Between Frogville and Huskey it turns back north before ending at US-70 near Fort Towson.

SH-109 originally ran from Fort Towson to Raymond Gary State Park.