What is the longest river in the United States?

The Missouri River is recognized as the longest river in the United States, stretching approximately 2,341 miles from its source in Montana through several states before it flows into the Mississippi River in Missouri. This length surpasses that of the other rivers mentioned in the options.

To provide context on the other rivers listed, the Mississippi River, while one of the most prominent and important rivers in the United States, is actually the second longest, measuring about 2,340 miles. The Colorado River is known for its dramatic canyons and is a vital water source in the southwestern U.S., but it is significantly shorter, at around 1,450 miles. The Hudson River, located in New York, is also much shorter than both the Missouri and Mississippi rivers, spanning approximately 315 miles. The distinguishing feature of the Missouri River is its length, which makes it the longest river in the U.S., further solidifying its significance in American geography.