The Mississippi River is 2,340 miles (3,767 km) long, making it the longest in the United States.
The Missouri River, at 2,315 miles (3,727 km) long, is the second longest, and together they form the fourth longest river system in the world.
The Missouri River begins its journey in the Rocky Mountains of southwestern Montana, and it joins the Mississippi River a few miles north of St. Louis, Missouri.
The Missouri River forms part of the state boundaries of South Dakota, Nebraska, Iowa, Missouri, and Kansas.
The Mississippi and its major tributaries drain a 1.2 million square mile (3.1 million square kilometers) area, covering all or part of 31 U.S. states.
In some places the river is 1.5 miles (2.4 km) wide.
Its source is Lake Itasca in Minnesota, and it empties into the Gulf of Mexico near New Orleans, Louisiana.