Campbell County, Georgia was created by the Georgia legislature in 1828 on December 20th. The land was taken from Fayette, Coweta, and Carroll counties, and from the half of DeKalb County which became Fulton County soon afterward. Georgia's Cherokee Land Lottery of 1832 also added to the county.
The original county seat was Campbellton, however when the Atlanta & West Point Railroad began to plan its route, the town's residents said no due to noise concerns. The tracks were laid through Fairburn instead, which flourished while Campbellton died out, and soon became the new county seat in 1870.
The northwestern half of Campbell (and a bit more of Carroll) became Douglas County in 1870, divided on October 17th at the Chattahoochee River. The remainder of Campbell County was ceded to Fulton at the end of 1931, along with Milton County, to save money during the Great Depression. The legislation creating the merger was enacted in 1929, on August 9th, with Milton being added to the process in 1931.
The map at right shows Campbell County (dark red) prior to the merger with Fulton. The county to the northwest of it is Douglas, formerly part of Campbell.