Decatur is the largest city and the county seat of Macon County in the U.S. state of Illinois, with a population of 76,122 as of the 2010 Census. The city was founded in 1829 and is situated along the Sangamon River and Lake Decatur in Central Illinois. Decatur's estimated population for 2019 was 70,746. Decatur is the thirteenth-most populous city in Illinois, and the state's sixth-most populous city outside the Chicago metropolitan area. Decatur is listed by the United States Census Bureau as number 3 in "The 15 Fastest-Declining Large Cities" which showed a 7.1% population loss of (-5,376) from 2010 to 2019.
The city is home of private Millikin University and public Richland Community College. Decatur has an economy based on industrial and agricultural commodity processing and production, including the North American headquarters of agricultural conglomerate Archer Daniels Midland, international agribusiness Tate & Lyle's largest corn-processing plant, and the designing and manufacturing facilities for Caterpillar Inc.'s wheel-tractor scrapers, compactors, large wheel loaders, mining class motor grader, off-highway trucks, and large mining trucks.
The city is named after War of 1812 naval hero Stephen Decatur.
Decatur is an affiliate of the U.S. Main Street program, in conjunction with the National Trust for Historic Preservation.
The Potawatomi Trail of Death passed through here in 1838.
Post No. 1 of the Grand Army of the Republic was founded by Civil War veterans in Decatur on April 6, 1866.