The southern terminus of LA 109 is located just north of I-10 (Exit 4) between Orange, Texas and Vinton, Louisiana.

From this four-way intersection, US 90 heads east toward Vinton and south a short distance to I-10 (Exit 4), at which point the two highways proceed west in a concurrency across the state line into Orange, Texas.

Meanwhile, LA 109 proceeds due north, immediately crossing the Union Pacific Railroad (UPRR) tracks, for 2.5 miles (4.0 km) and intersects LA 3063, which heads east to the Delta Downs Race Track and ultimately into Vinton.

Continuing north for 4.2 miles (6.8 km), LA 109 crosses the Sabine River Diversion System and curves slightly to the northwest for about the same distance to reach the community of Starks.

[5][6][7] LA 109 was created with the 1955 Louisiana Highway renumbering,[8] and its route has remained unchanged to the present day.