The Longest River in the U.S.
The longest river in the United States is the Missouri River. It runs for about 2,341 miles. Its source is high in the Rocky Mountains of Montana, and from there it flows generally east and south across the Great Plains until it joins the Mississippi River near St. Louis.
A Close Race with the Mississippi
The Missouri is sometimes confused with the Mississippi, and for good reason. The two rivers are very close in length, and the Missouri is actually a tributary of the Mississippi - it flows into it rather than reaching the sea on its own. Together, the combined Missouri and Mississippi form one of the longest river systems in the entire world.
A River of History
The Missouri has played a huge role in American history. It served as a major route for exploration and trade as the country expanded westward, and the famous Lewis and Clark expedition followed it on their journey across the continent. Its nickname, the "Big Muddy," comes from the heavy load of silt its waters carry. Today its basin contains a large share of American farmland.
Source
This article was written using information from Wikipedia.