DeKalb was established as Georgia's 56th county and is situated on a natural ridge that runs between Atlanta and Athens, the Continental Divide. The southern boundary is the South River and the northern boundary is the Hightower Trail, a trading path used by Indians. The county has 269 square miles. DeKalb was established from parts of Henry, Fayette and Gwinnett Counties with the General Assembly of the State of Georgia appointing five commissioners who picked land lot 246 in the 15th militia district as the county site. The county was named after Baron Johann de Kolb, a native of Germany and self proclaimed baron who aided the colonists in their fight for independence. The county seat land lot 246 was named for Stephen Decatur, a naval hero in the War of 1812. DeKalb was already organized into militia districts with justices of the Inferior Courts and justices of the peace retained their offices. Captains of the militia districts often served as judges and tax collectors for the districts as well. Some of these early militia districts included the Diamond District, the Browning District and the Shallowford District. The City of Atlanta, in its infancy and until 1853 when Fulton County was created, was entirely in DeKalb County.
The early settlers of DeKalb were of English, Scotch and Irish descent coming from Virginia and the Carolinas. They were subsistence farmers who were not highly educated and usually lived in log cabins.
Decatur was incorporated as the county seat on December 10, 1823. Its location was a trading post at the intersection of two Indian trails.
In July of 1864, DeKalb had its first taste of the war; much of the battle of Atlanta actually took place in DeKalb County around the Courthouse and along DeKalb Avenue.
Chief of the industries during the early years in DeKalb were granite quarrying, farming, dairy farming and cotton mills and grain mills. Land near the South River produced 1000 or more pounds of cotton per acre, and the county was one of the largest milk producers in the southeast. Large truck farms supplied vegetables throughout the region. Development in DeKalb in the early years was along the rivers and along the railroads from Decatur, east to Stone Mountain and south east to Lithonia.