It is part of a three-state multistate route beginning in Florida and ending in South Carolina.

Shortly afterwards, US 301/SR 23 split from the other routes, while US 1/US 23/SR 4/SR 15/SR 121 stay concurrent until Racepond, where US 1/US 23/SR 4 continue to the northwest while SR 15/SR 121 branch off to the northeast.

In Augusta, SR 121 travels concurrently with US 1/US 25/US 78/US 278/SR 10 along Gordon Highway and serves as a major road.

[1] In 2004, the Senate and Georgia House of Representatives of the state of Georgia passed legislation designating SR 121 as the Woodpecker Trail Highway from the Florida state line to the South Carolina state line and was signed into law by Governor Sonny Perdue on May 17, 2004.

On September 19, 2005, Governor Perdue and others officially dedicated the Woodpecker Trail Highway in Augusta.

[2] The origin of the trail's name dates back to the 1920s when it was listed by AAA, and, in the 1940s, highway signs using Walter Lantz's Woody Woodpecker character marked the highway but eventually fell out of use.

[2] Of course, it was in use before then, maybe as early as 1915 by Native Americans, horse-drawn buggies, and the first horseless carriages.

In 1952, an unnumbered road was established from Camp Cornelia east to SR 23 south-southwest of Folkston.