Irwin County, the 45th county created, retains only a small portion of the territory given to it when it was formed from Creek Indian lands in 1818. It once encompassed all of south central Georgia, but now contains the upper reaches of the Alapaha, Willacoochee and Satilla rivers.
Irwin County was named for Governor Jared Irwin, a North Carolina native. Irwin was famous for his opposition to the Yazoo Law of 1795, by which the state of Georgia sold a vast tract of land at one and a half cents per acre to several companies, including one owned in part by a U.S. Senator. Irwin rescinded the law in 1796 during his term as governor.
During the Civil War, Irwinville to the northeast of Ocilla was the county seat, and the location where Union soldiers captured Jefferson Davis. The site is now the Jefferson Davis Park and Museum.
Ocilla is a version of an old Indian name, Osceola. The county's first courthouse was constructed in 1848-1849, and the one currently in use was built in 1905.