Chicago is the center of the Midwest, geographically and culturally. Always has been. Draw a big circle around Chicago, and that's roughly your Midwest states. Another good proxy for the Midwest is to look at the original members of the Big 10 athletic conference.

Indiana, Illinois, Wisconsin, Michigan, Ohio, Iowa, and Minnesota are the Midwestern states. Maybe some of Nebraska and the edge of Kansas and Missouri, but that's as far as it goes.

https://en.wikipedia.org/wiki/Midwestern_United_States

Before 1803, The Mississippi River was the Far West of the contiguous US terrirory.

New Orleans & further west still belonged to France.

Ohio and Indiana were known as the Midwest since they were about halfway to the Mississippi from the east coast.

Part of Kentucky is very close to Ohio & Indiana and the rest were Southern States.

Now Illinois, Wisconsin, Minnesota, Iowa and part of Missouri seem to have snuck in somehow but Dakota, Newbraska and Kansas are highly exaggerating.

No doubt Oklahoma and Texas are in The West, with almost all of Texas being part of the Southwest.

Midwesterners represent more like a regional/cultural designation than their geographical location, although both features do apply.

Western Pennsylvania is not very much like the East Coast either.

I think your distinction is Upper Midwest vs. the legacy Northwest Territory/"Great Lakes" states. Midwest to outsiders seems to be a catch-all for "not West, not South, but west of the Appalachians" when in reality it's a mix of Great Lakes, Great Plains, and other gradients of other regions.

I'd say that anything north of the 618 area code would be very midwest, but once you get roughly south of I-70 the vibe is much more southern.

Of course, urban midwest can be very different indeed from rural midwest.