Lee Sigelman refers to himself as a “midwesterner” even though he lives in D.C. This reminds me that we want to redo our geography-and-voting analyses looking at the states where people come from (rather than where people currently live). A bunch of surveys ask this, I think.
More generally, I assume that some sociologists have looked at the question of how people define themselves by region. I know there’s been lots of research on people’s racial, ethnic, and national self-definition. I remember that, about 15 years ago, Michael Hout gave a talk in our seminar: “How 4 million Irish immigrants became 40 million Irish Americans.” Contrary to expectations, it wasn’t about prolific breeding, it was about how people of mixed background choose to classify themselves. (Maybe things are different now, in the era of Caublanasians.)
You can take the boy out of Watertown, South Dakota, but you can't take Watertown, South Dakota out of the boy. Anyway, I like your idea for an ananysis and may even steal it from you (without attribution, of course).
South Dakota is not in the Midwest. It is a Plains State.
The Midwest is Ohio, Kentucky, Indiana, Michigan, Wisconsin, Minnesota, and Iowa. (We are geographically impaired as well, or the Mississippi is too wide for us to cross.)
There are (weak) arguments to be made for Missouri—most of them are based on the Cubs-Cardinals rivalry from the days when they dominated the South and everything West of the Mississippi where (White) baseball was concerned—though they generally get you on a slippery slope toward Kansas, which is clearly a Plains State.