Osceola is a city in St. Clair County, Missouri, United States. The population was 947 at the 2010 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 land 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 all the tribe's land in Missouri. With the way cleared for non-native settlers, more people began to arrive in the St.