Owatonna is a city in Steele County, Minnesota, United States. The population was 25,599 at the 2010 census. It is the county seat of Steele County. Owatonna is home to the Steele County Fairgrounds, which hosts the Steele County Free Fair in August.Interstate 35 and U.S. Highways 14, and 218 are three of the main routes in the city.