I thought maybe I was misremembering this, so I checked on MapQuest.
While the Mississippi river forms most of the western border of the state of Mississippi, it doesn’t really flow THROUGH the state (oxbows and other quirks aside).
The terminus of what looks like the main channel is in Louisiana, SE of New Orleans. So, at least part of (and maybe all of) the delta is in Louisiana.
Yep…the only three states the Mississippi flows through, as opposed to cutting teensy pieces off and tacking them “across” the river, are Minnesota, Illinois, and Louisiana, and Illinois only qualifies due to that one township that insisted on staying in Illinois when it got cut off (a la the teensy pieces) and attached to Missouri.