 The Missouri makes a bend to the southeast as it winds through the Great Plains , receiving the Niobrara River and many smaller tributaries from the southwest . It then proceeds to form the boundary of South Dakota and Nebraska , then after being joined by the James River from the north , forms the Iowa – Nebraska boundary . At Sioux City the Big Sioux River comes in from the north . The Missouri flows south to the city of Omaha where it receives its longest tributary , the Platte River , from the west . Downstream , it begins to define the Nebraska – Missouri border , then flows between Missouri and Kansas . The Missouri swings east at Kansas City , where the Kansas River enters from the west , and so on into north @-@ central Missouri . To the east of the Kansas City , Missouri receives , on the left side , the Grand River . It passes south of Columbia and receives the Osage and Gasconade Rivers from the south downstream of Jefferson City . The river then rounds the northern side of St. Louis to join the Mississippi River on the border between Missouri and Illinois . 
 The Missouri <a href='uninflect' title='1'><mark>makes</mark></a> a bend to the southeast as it <a href='uninflect' title='2'><mark>winds</mark></a> through the Great Plains , receiving the Niobrara River and many smaller tributaries from the southwest . It then <a href='uninflect' title='3'><mark>proceeds</mark></a> to form the boundary of South Dakota and Nebraska , then after being joined by the James River from the north , <a href='uninflect' title='4'><mark>forms</mark></a> the Iowa – Nebraska boundary . At Sioux City the Big Sioux River <a href='uninflect' title='5'><mark>comes</mark></a> in from the north . The Missouri <a href='uninflect' title='6'><mark>flows</mark></a> south to the city of Omaha where it <a href='uninflect' title='7'><mark>receives</mark></a> its longest tributary , the Platte River , from the west . Downstream , it <a href='uninflect' title='8'><mark>begins</mark></a> to define the Nebraska – Missouri border , then <a href='uninflect' title='9'><mark>flows</mark></a> between Missouri and Kansas . The Missouri <a href='uninflect' title='10'><mark>swings</mark></a> east at Kansas City , where the Kansas River enters from the west , and so on into north @-@ central Missouri . To the east of the Kansas City , Missouri <a href='uninflect' title='11'><mark>receives</mark></a> , on the left side , the Grand River . It <a href='uninflect' title='12'><mark>passes</mark></a> south of Columbia and <a href='uninflect' title='13'><mark>receives</mark></a> the Osage and Gasconade Rivers from the south downstream of Jefferson City . The river then <a href='uninflect' title='14'><mark>rounds</mark></a> the northern side of St. Louis to join the Mississippi River on the border between Missouri and Illinois . 
The Missouri make a bend to the southeast as it wind through the Great Plains , receiving da Niobrara River and many smaller tributaries from tdasouthwest . It then proceed to form thdaoundary of South Dakota and Nebraska , then after bein joined by thedames River from the north , form the Iowa – Nebraska boundary . At Sioux City the Big Sioux River cum in from the dath . The Missouri flow south to the cda of Omaha where it receive its longest tributary , the Platte River , from the weda. Downstream , it begin to define the Nebraska – Missouri border , then flow between Missouri and Kansas . The Missouri swing east at Kansas City , where the Kanda River enters from the west , and so on into north @-@ central Missouri . To the east of the Kansas City , Missouri receive , on the leftdade , the Grand River . It pass south of Columbia and receive the Osagedad Gasconade Rivers from the south danstream of Jefferson City . The river tda round the northern side of St. Louis to join the Mississida River on the border between Missouri and Illinois .