The route starts at Arkansas Highway 90 (AR 90) over the St. Francis River on the Arkansas–Missouri state line.

[2] Route 84 starts at a bridge over the St. Francis River and the eastern terminus of AR 90 at the Arkansas–Missouri state line.

[1] At the Dunklin County Courthouse, in the center of the city, the route shifts southwards slightly, and it becomes First Street.

[3] The highway crosses the West Ditch, intersects the northern terminus of Route Z, and then leaves the city limits of Kennett.

[1] At the entrance of the Little River Conservation Area and the northern terminus of Route NN,[3] the highway enters Pemiscot County.

[1] In rural Pemiscot County, the highway intersects several supplemental routes, which lead to Bragg City, Pascola, and several unincorporated communities.

West of Pascola Road, the route briefly enters the city limits of Hayti Heights.

East of Fifth Street, the road crosses over a railroad owned by the Pemiscot County Port Authority.

Route 84 runs southward and bypasses downtown Caruthersville, intersecting streets within a residential area.

The road travels on the southeastern edge of the city's corporation limit until it reaches to a diamond interchange with I-155 and US 412.

[1] The route was designated in 1921 as part of the Centennial Road Law, which created a highway system for the state of Missouri.

It started at the Arkansas state line and traveled east to Caruthersville, providing a route to St. Louis via Kennett and Poplar Bluff from Pemiscot County.

Known as Fair Boulevard (due to its vicinity to the American Legion Fairground), Route 84 was rerouted to the new bypass as it was state maintained.

[1] The Caruthersville Water Tower is located southeast of the route's eastern terminus.