is South Dakota a Midwestern state

[TDAS04]

Yes. If we’re dividing the United States into four regions and each state must belong to one region in its entirety, then South Dakota is a Midwestern state. If we can ignore state boundaries, then I’d personally refer to West River as “Western.”

Even though West River is slightly larger in land area than East River, South Dakota is Midwestern state on balance because most of the state’s population resides east of the Missouri River. The east generally dominates the state culturally.

[TDAS04]

Not that Ohio isn’t also a Midwestern state, this would be a better question if asked about the Buckeye State. Ohio’s Eastern tendencies are clear. That state is more similar to Pennsylvania—and, dear I say it, even New Jersey—than it is to Iowa or Illinois. Cleveland is very much an Eastern city.