Peoria (/piˈɔːriə/ 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 maize, 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.