State Route 12 (SR 12) is a state highway that runs west-to-east through portions of DeKalb, Rockdale, Newton, Morgan, Greene, Taliaferro, Warren, and McDuffie counties in central and eastern Georgia. The route runs from its western terminus at US 278 and SR 10 in Avondale Estates to its eastern terminus at US 78, US 278, and SR 10 in Thomson.

SR 12 runs concurrent with US 278 for its entire length. It is also concurrent with I-20/SR 402 from Exit 75, which is SR 124 (Turner Hill Road) in Lithonia until it reaches Exit 90 in Covington in Newton County. SR 12 largely runs parallel to I-20 from DeKalb County, near Atlanta, to McDuffie County.

The route starts on the eastern edge of Avondale Estates in DeKalb County and initially runs southeast, crossing I-285 shortly after its departure. SR 12 continues through Lithonia, where it merges with and is co-signed with I-20 through Conyers and Rockdale County to Covington in Newton County. In Covington, SR 14 and US 278 split from I-20 and parallel the interstate on its southern side in an easterly direction to south of Social Circle, where the two routes cross I-20 and continue to parallel the interstate, now on its northern side.

The routes continues into Morgan County and runs through Rutledge and Madison into Greene County, heading through Greensboro and Union Point on its way further east into Taliaferro County and Crawfordville. From Crawfordville the route heads southeast, crosses into Warren County, and crosses I-20 to its southern side once again south of Sharon. SR 12 continues south into Warrenton, turns northeast, and runs to its eastern terminus in Thomson in McDuffie County.