Peoria ( pee-OR-ee-ə) is a city in and county seat of Peoria County, Illinois, United States. Located on the Illinois River, the city had a population of 113,150 as of the 2020 census, making it the eighth-most populous city in Illinois. It is the principal city of the Peoria metropolitan area in Central Illinois, consisting of the counties of Fulton, Marshall, Peoria, Stark, Tazewell, and Woodford which had a population of 402,391 in 2020.

Established in 1691 by the French explorer Henri de Tonti, Peoria is the oldest permanent European settlement in Illinois, according to the Illinois State Archaeological Survey. Originally known as Fort Clark, it received its current name when the County of Peoria was organized in 1825. The city was named after the Peoria people, a member of the Illinois Confederation. On October 16, 1854, Abraham Lincoln made his Peoria speech against the Kansas-Nebraska Act. Prior to prohibition, Peoria was the center of the whiskey industry in the United States. More than 12 distilleries operated in Peoria by the end of the 19th century, more than any other city in the U.S.

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; the company relocated its headquarters to Deerfield, Illinois in 2018, and then Irving, Texas, in 2022.

The city is associated with the phrase "Will it play in Peoria?", which may have originated from the vaudeville era and is often spuriously attributed to Groucho Marx. Museums in the city include the Peoria Riverfront Museum, the Pettengill–Morron House and the John C. Flanagan House (both of which are managed by the Peoria Historical Society), and the Peoria Playhouse Children's Museum. Wheels o' Time Museum is near Peoria.