Decatur, incorporated in 1836, is the county seat of Macon County, Illinois, USA. As of the 2000 census, the city had a total population of 81,860, but a 2003 estimate showed the population dipped to 79,285. It is the county seat of Macon County^GR6. This town is named after War of 1812 naval hero Stephen Decatur, Jr.

The city's motto is "Decatur, We Like it Here" . The old motto was "The Pride of the Prairie". "The Soybean Capital of the World" is the unofficial motto. The city symbol is the Transfer House, an early 20th century Victorian structure originally located in the center of town where the city's mass transit lines met. The Transfer House was moved in 1963 to save it from destruction as roads were being built for the increasing automobile traffic. There is currently an effort, led by mayor Paul Osborne, to return the Transfer House to its original location.

Decatur is the location of Millikin University, founded by James Millikin. The city is largely industrial in character, with production facilities for Caterpillar, Archer Daniels Midland, and Tate & Lyle (previously A. E. Staley). The Firestone factory in Decatur closed at the end of 2001 after the dispute with Ford Motor Company. In the transition from a manufacturing to a service economy, Decatur has experienced significant population loss: in 1980, the population was 94,081.