Pendersleigh & Sons' Official Map of Missouri
In my experience, when you'ins tell people you’re from Missouri, most people reply self-satisfiedly with "don't you mean Missouruh?" or, alternately, "where is Missouri? I don’t think I’ve ever been there."
Whether Missouri is Lower Midwestern or Upper Southern (or the Border South or, the Upland South, or less commonly today, the Yeoman South) is a somewhat common debate amongst Missourians... at least on the internet.
In my experience, Missouri's Midwestern neighbors, centered along the Great Lakes, (haters) tend to disparage Mighty Mo as a hick state whurr test scores are low, the accent is ugly and you'ins can buy fireworks, liquor and ammo... all in the same place.
Missouri's neighbors in the Deep South (also haters) usually don't consider it to be Southern because Missouri didn't side with the South in the Civil War (well, that's complicated-- thurr were 30,000 gray and 109,000 blue) and because South Coasters love to equate the entire South with just the Deep South aka the Lower South aka the Plantation South.
As far as Southern credentials go, Mark Twain, Langston Hughes, Thomas Hart Benton all seem fairly Southern, do they not? On the other hand, natives like T.S. Elliot, William Burroughs and Maya Angelou don’t so much, huh? Cultural cringe I reckon, plays a part in this confusion, as do geographical overlap and historical shifts.