DeKalb County is located in the north central portion of the U.S. state of Georgia. As of the 2020 census, the population was 764,382, making it Georgia's fourth-most populous county. Its county seat is Decatur.

Decatur is a city in, and the county seat of, DeKalb County, Georgia, United States, part of the Atlanta metropolitan area. With a population of 24,928 in the 2020 census, the municipality is sometimes assumed to be larger since multiple ZIP Codes in unincorporated DeKalb County bear Decatur as the address. The city is served by three MARTA rail stations. The city is located approximately five miles northeast of Downtown Atlanta and shares its western border with both the city of Atlanta and unincorporated DeKalb County. The Druid Hills neighborhood is to the northwest of Decatur.