 In 1990 , the Missouri River watershed was home to about 12 million people . This included the entire population of the U.S. state of Nebraska , parts of the U.S. states of Colorado , Iowa , Kansas , Minnesota , Missouri , Montana , North Dakota , South Dakota , and Wyoming , and small southern portions of the Canadian provinces of Alberta and Saskatchewan . The watershed 's largest city is Denver , Colorado , with a population of more than six hundred thousand . Denver is the main city of the Front Range Urban Corridor whose cities had a combined population of over four million in 2005 , making it the largest metropolitan area in the Missouri River basin . Other major population centers – mostly located in the southeastern portion of the watershed – include Omaha , Nebraska , situated north of the confluence of the Missouri and Platte Rivers ; Kansas City , Missouri – Kansas City , Kansas , located at the confluence of the Missouri with the Kansas River ; and the St. Louis metropolitan area , situated south of the Missouri River just below the latter 's mouth , on the Mississippi . In contrast , the northwestern part of the watershed is sparsely populated . However , many northwestern cities , such as <unk> , Montana , are among the fastest growing in the Missouri basin . 
