Osceola is a city and the county seat of Clarke County, Iowa, United States. The population was 5,415 at the time of the 2020 census. Osceola was named after a Seminole Indian leader of the same name. Osceola is an anglicised form of Asiyahola: assi, from a ceremonial yaupon holly tea or "black drink" and yaholi, the name of a Creek god intoned when the drink was served.