With a population of 24,928 in the 2020 census,[4] the municipality is sometimes assumed to be larger since multiple ZIP Codes in unincorporated DeKalb County bear Decatur as the address.

Decatur was established at the intersection of two Native American trails: the Sandtown, which led east from the Chattahoochee River at Utoy Creek, and the Shallowford, which follows today's Clairmont Road, and eventually crossed near Roswell.

In July 1864, Major-General James McPherson occupied the town to cut off the Confederates' supply line from Augusta.

We attacked Decatur on the 22d and took the town driving out a Brigade of Infantry and a good deal of Dismounted Cavalry.

Our loss about seventy killed and wounded.In the second half of the twentieth century the metropolitan area of Atlanta expanded into unincorporated DeKalb County, eventually surrounding two sides of the town of Decatur.

Over the past twenty years, it has gained a local and national reputation as a progressive city with a high level of citizen involvement.

Decatur is bordered by Avondale Estates to the southeast and Atlanta to the southwest, and unincorporated DeKalb County elsewhere.

[12] St. Peter Claver Regional School has a Decatur mailing address but is in nearby Candler-McAfee CDP.

At their organizational meeting each January, the Commissioners elect a mayor and mayor-pro-tem from among their own membership for a one-year term.

[22] Previous mayors have included Leslie Jasper Steele (1915), Jack Hamilton, Walter Drake, Mike Mears, Ann A. Crichton, Elizabeth Wilson, William Floyd, Jim Baskett and Scott Candler, Sr. (known as Mr. DeKalb).

Other events throughout the year include parades, Concerts on the Square, wine crawls, art walks, runs, and races.

[29] Decatur's downtown area and residential neighborhoods are filled with historic structures and sites of interest.

This list primarily consists of structures on the National Register of Historic Places, but many remain privately owned and may only be viewed from the exterior.