Decatur
- County:
- Macon County
- County Seat:
- Yes
- Area (mi²):
- 44.163
- State:
- Illinois
Decatur is a city located in Macon County, Illinois. Decatur has a 2026 population of 68,763. It is also the county seat of Macon County. Decatur is currently declining at a rate of -0.09% annually and its population has decreased by -3.12% since the most recent census, which recorded a population of 70,978 in 2020.