Decatur is the largest city and the county seat of Macon County in the U.S. state of Illinois, with a population of 70,522 as of the 2020 Census. The city was founded in 1829 and is situated along the Sangamon River and Lake Decatur in Central Illinois. Decatur is the seventeenth-most populous city in Illinois.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.

Springfield is the capital of the U.S. state of Illinois and the county seat and largest city of Sangamon County. The city's population was 116,250 at the 2010 U.S. Census, which makes it the state's sixth most-populous city, the second largest outside of the Chicago metropolitan area (after Rockford), and the largest in central Illinois. As of 2019, the city's population was estimated to have decreased to 114,230, with just over 211,700 residents living in the Springfield Metropolitan Statistical Area, which includes Sangamon County and the adjacent Menard County.Present-day Springfield was settled by European Americans in the late 1810s, around the time Illinois became a state. The most famous historic resident was Abraham Lincoln, who lived in Springfield from 1837 until 1861, when he went to the White House as President of the United States. Major tourist attractions include multiple sites connected with Lincoln including the Abraham Lincoln Presidential Library and Museum, Lincoln Home National Historic Site, Lincoln-Herndon Law Offices State Historic Site, and the Lincoln Tomb at Oak Ridge Cemetery. The city lies in a valley and plain near the Sangamon River. Lake Springfield, a large artificial lake owned by the City Water, Light & Power company (CWLP), supplies the city with recreation and drinking water. Weather is fairly typical for middle latitude locations, with four distinct seasons, including, hot summers and cold winters. Spring and summer weather is like that of most midwestern cities; severe thunderstorms may occur. Tornadoes hit the Springfield area in 1957 and 2006. The city has a mayor–council form of government and governs the Capital Township. The government of the state of Illinois is based in Springfield. State government institutions include the Illinois General Assembly, the Illinois Supreme Court and the Office of the Governor of Illinois. There are three public and three private high schools in Springfield. Public schools in Springfield are operated by District No. 186. Springfield's economy is dominated by government jobs, plus the related lobbyists and firms that deal with the state and county governments and justice system, and health care and medicine.

Illinois (IL-ə-NOY) is a state in the Midwestern region of the United States. It has the fifth largest gross domestic product (GDP),the sixth largest population, and the 25th largest land area of all U.S. states.

Peoria ( pee-OR-ee-ə) is the county seat of Peoria County, Illinois, and the largest city on the Illinois River. As of the 2010 census, the city had a population of 115,007. It is the principal city of the Peoria Metropolitan Area in Central Illinois, consisting of the counties of Marshall, Peoria, Stark, Tazewell, and Woodford, which had a population of 373,590 in 2011. Established in 1691 by the French explorer Henri de Tonti, Peoria was later labeled by the Peoria Historical Society to be the oldest European settlement in Illinois. Originally known as Fort Clark, it received its current name when the County of Peoria organized in 1825. The city was named after the Peoria tribe, a member of the Illinois Confederation. On October 16, 1854, Abraham Lincoln made his Peoria speech against the Kansas-Nebraska Act.A major port on the Illinois River, Peoria is a trading and shipping center for a large agricultural area that produces corn, soybeans, and livestock. Although the economy is well diversified, the city's traditional manufacturing industries remain important and produce earthmoving equipment, metal products, lawn-care equipment, labels, steel towers, farm equipment, building materials, steel, wire, and chemicals. Until 2018, Peoria was the global and national headquarters for heavy equipment and engine manufacturer Caterpillar Inc., one of the 30 companies composing the Dow Jones Industrial Average, and listed on the Fortune 100; in the latter year, the company relocated its headquarters to Deerfield, Illinois.The city is associated with the phrase "Will it play in Peoria?", which originated from the vaudeville era and was popularized by Groucho Marx. Museums in the city include the Pettengill-Morron House, the John C. Flanagan House, and the Peoria Riverfront Museum.