The Missouri river joins the Mississippi at St. Louis.
At Cairo, Illinois, the Ohio joins the Mississippi. The three states that have borders there are Illinois (to the NE), Kentucky (to the SE) and Missouri (to the W).
Missouri, Illinois, and Kentucky.
Missouri, Kentucky, and Illinois
Lake Erie
The Missouri River joins the Mississippi very near St Louis.
Kentucky, Indiana, Illinois
Mississippi River
The confluence of the Ohio and Mississippi is essentially the Missouri-Illinois-Kentucky "triple point".
The Missouri joins the Mississippi near St. Louis, Missouri.
Indiana, Ohio, and Illinois
missouri