Missouri is a state in the Midwestern United States .  With over six million residents, it is the 18th-most populous state of the Union. The largest urban areas are Kansas City , St. Louis , Springfield , and Columbia ; the capital is Jefferson City , near the center of the state on the Missouri River . The state is the 21st-most extensive in area. In the South are the Ozarks , a forested highland, providing timber, minerals, and recreation. The Mississippi River forms the eastern border of the state.