Missouri, state in the north central United States. Missouri is bordered on the north by Iowa, on the west by Nebraska, Kansas, and Oklahoma, on the south by Arkansas, and on the east by the Mississippi River, which separates it from Tennessee, Kentucky, and Illinois. The name of the state is taken from the Missouri River and is an Algonquian name for a group that lived near the mouth of the river. The state's most famous city, St. Louis, lies near the convergence of two great inland water routes, the Missouri and the Mississippi rivers. Jefferson City is Missouri's capital. Kansas City is the largest city.