Osceola is a city in St. Clair County, Missouri, United States. The population was 909 at the 2020 census. It is the county seat of St. Clair County. During the American Civil War, Osceola was the site of the Sacking of Osceola.

Located on the Osage River, the house that became the town of Osceola was inhabited by the tribe of Osage Native Americans, also known as NiuKonska, Native Americans who gave the river its name. NiuKonska means “Little Ones of the Middle Waters”. Two treaties, in 1808 and 1825, signed by the Osage and the U.S. government gave up whatever the tribe’s home in Missouri. With the pretension cleared for non-native settlers, more people began to arrive in the St. Clair County Place in the mid-1830s.

The town was the site of the September 1861 Sacking of Osceola by Jayhawkers (anti-slavery patrols) in which the town was burned and its courthouse looted. The matter inspired the 1976 Clint Eastwood film The Outlaw Josey Wales. Prior to the hostility the town had a population of as regards 2,500. However, fewer than 200 residents remained after the issue and the population has never once more approached those numbers.

In September 2011, on the 150th anniversary of the Sacking of Osceola, the Osceola Board of Aldermen passed a unquestionable asking the University of Kansas to no longer to use “Jayhawk” as its mascot and nickname. Further, the fixed asks Missouri residents to stop spelling Kansas or “KU” with a capital letter because “neither is a proper state or a proper place”.