Two rivers that join the Mississippi River are the Missouri River and the Ohio River.
The confluence of the Alleghaney and Monogahela Rivers form the Ohio River at Point State Park in Pittsburgh. Thus the three rivers that "come together" at that point are the Ohio, Allegahaney and Monogahela.
Both the Illinois & Missouri rivers join the Mississippi river near St. Louis, Missouri.
The tributaries of a river are the streams or smaller rivers that join the main river. for example, the Missouri River is the chief tributary of the Mississippi.
The Arkansas River arises in Colorado and still has that name when it flows into the Mississippi. It's the only Colorado river I know of that flows directly into the Mississippi. The Platte (both the North and South) arise in Colorado and join in Nebraska before flowing into the Missouri, which then joins the Mississippi. The Republican and Smoky Hill Rivers join in Kansas to form the Kansas River, which then flows into the Missouri and thence the Mississippi. All other significant Colorado rivers that don't join one of the above either wind up in the Rio Grande or the Colorado River, neither of which ever joins the Mississippi.
The Allegheny and Monogahela rivers join at the confluence to form the Ohio River.
Mississippi
mississippi/missouri
The major tributary of the Mississippi River that flows in the southeasterly direction to join the Mississippi River near St. Louis is the Missouri River. The Missouri River and the Mississippi River join at the border between Missouri and Illinois.
the Congo river
They meet near St. Louis, Missouri.St. LouisThe Missouri River flows into the Mississippi River just north of Saint Louis, Missouri.
Two two largest Tributaries of the Mississippi River are the Missouri River and the Ohio River. The Missouri River intersection is just below St. Louis and essentially doubles the size of the River. The Ohio River (which is joined by both the Cumberland River at Smithland Ky. and the Tennessee River at Paducah Kentucky) joins the Mississippi River at Cairo, Illinois about 950 Miles above the Head of the Passes. The Ohio River combined with the Mississippi forms what is referred to as the lower Mississippi River and again it doubles in size. There are no locks and dams on the lower Mississippi River. The Ohio River is actually as wide if not wider than the Mississippi River at their junction. A large part of that is due to the Cumberland and Tennessee Rivers both very large Rivers in themselves joining the Ohio. The Cumberland joins about 62 miles above the mouth of the Ohio and the Tennessee joins the Ohio River only about 50 miles above the junction with the Mississippi River. Two more good size rivers the Illinois River joins the Upper Mississippi and the Arkansas River joins the lower. There are many more smaller rivers which join. I answered this in a question naming all the Tributaries of the Mississippi River. Captain Jim Turner