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.
In 2017, the city's estimated population was 72,174. The city is home of private Millikin University and public Richland Community College. Decatur has vast industrial and agricultural processing 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, off-highway trucks, and large mining trucks. Decatur is located at 39°51′6″N 88°56′39″W (39. 851636, −88. 944228). Decatur is 180 miles southwest of Chicago, 40 miles east of Springfield, the state capital, and 115 miles northeast of St. Louis. According to the 2010 census, Decatur has an area of 46. 91 square miles (121. 50 km2), of which 42. 22 square miles (109. 35 km2) (or 90%) is land and 4. 69 square miles (12. 15 km2) (or 10%) is water. Lakes include Lake Decatur, formed in 1923 by the damming of the Sangamon River. The Decatur Metropolitan Statistical Area (population 109,900) includes surrounding towns of Argenta, Boody, Blue Mound, Elwin, Forsyth, Harristown, Long Creek, Macon, Maroa, Mount Zion, Niantic, Oakley, Oreana, and Warrensburg.