U.S. Route 78N (US 78N) was a northern divided U.S. highway that comprised the current mainline of US 78 from Heflin, Alabama, to Villa Rica, Georgia.

The road that would eventually become US 78N was established in 1920, as SR 8 from the Alabama state line to Villa Rica.

[1][6] The next year, US 78 split into two divided routes, with US 78N being designated from Heflin to Villa Rica, on the northern segment of SR 8 (thereby replacing the mainline highway).

The road that would eventually become US 78 was established in 1920 as part of SR 34 from Carrollton to Villa Rica.

[5] By the end of the third quarter of 1921, SR 16 was designated from the Alabama state line, west of Bowdon to Carrollton.

[1][6] In 1927, US 78 split into two divided routes, with US 78S being designated from Heflin to Villa Rica, via Bowdon and Carrollton, on the southern branch of SR 8.

The road that would eventually become US 78 Alternate was established in 1920 as part of SR 34 from Carrollton to Villa Rica.

[5] By the end of the third quarter of 1921, SR 16 was designated from the Alabama state line, west of Bowdon to Carrollton.

[1][6] In 1927, US 78 split into two divided routes, with US 78S being designated from Heflin to Villa Rica, via Bowdon and Carrollton, on the southern branch of SR 8.

in the Athens – Clarke County metropolitan area is a Bannered U.S. Highway that is concurrent with Georgia State Route 10 (SR 10) for its entire length.

North Avenue and Thomas Street had their state route designation removed.

is a 4.6-mile-long (7.4 km) business route of US 78 that exists entirely within the south-central part of Wilkes County.

At Depot Street, they are about one block north of the northern terminus of the Georgia Woodlands Railroad line.

Between Spring Street and Cheney Parkway, the three highways pass by the town square.

Immediately after that intersection, the four highways curve to the southeast and pass the Washington–Wilkes Historical Museum.

is a short business loop in the central part of the town of Blackville, via Walker and Main Streets.

[36] Even though it is signed west of South Carolina Highway 3 (SC 3; Solomon Blatt Avenue), the South Carolina Department of Transportation only includes the portion east of SC 3 as part of the business route.

[35] Originally, US 78 traversed along the route until by 1967, when new road south was created, allowing it to bypass Main Street.

It connects South Carolina Highway 61 (SC 61), at a point just southeast of its northern terminus, with US 78.