Constituent state of the United States of America. To the north lies Iowa; across the Mississippi River to the east, Illinois, Kentucky, and Tennessee; to the south, Arkansas; and to the west, Oklahoma, Kansas, and Nebraska. With the exception of Tennessee, Missouri has more neighbouring states than any other U.S. state. The area of Missouri is 69,697 square miles (180,516 square kilometres). Slightly more than half of the population lives in the two major cities, St. Louis and Kansas City, and their surrounding counties. Jefferson City is the capital.

Missouri was the westernmost state of the nation until the admission of Texas in 1845, and for decades it served as the eastern terminus of the Santa Fe and Oregon trails. For the West, St. Louis, Missouri's largest city, long was the closest contact with the more settled society and the culture of the East, and for the East the state had a reputation as the chief gateway to the West.

The Missouri River cuts across the state from Kansas City in the west, through Jefferson City in the centre, to just above St. Louis in the east, where the river joins the Mississippi. Missouri was the name of a group of Indians who lived in the area; the French gave the name to the river, and it was later transferred to the state.