Since it seems like you answered your own, here's one:
Name: Wiley County
Location: Midwest, similar location to Northern IL, IN and Southern WI, MI
Population: 400,000
Largest City: Lake Luciole (90,000)
Demographics: 84% White (mostly German, English and Scandinavian), 8% Asian (mostly Chinese, Indian, and Pakistani), 7% Latino (mostly Mexican and Central American) and 1% Black (mostly ADOS but an above average African immigrant pop.)
MHI: $80,000
Geography: Runs the gamut from inner ring suburbs of the nearby major city to outer ring exurbs. Has a sizable east-west divide, with the western suburbs being extremely rich and white while the eastern suburbs are more middle class and somewhat diverse in places.
History: Was settled early on by German Catholics with a smattering of Yankee abolitionists. Little industry, was primarily agricultural. Suburbanization started early in the inner ring streetcar suburbs in the far north of the county, around the 20s, but really picked up after WW2. Very white flight in character, and was also a center of evangelical culture.
That sounds like Waukesha County to me (the name even has the same first letter), so as Waukesha County goes, so goes Wiley. It's trending Dem at a dignified and deliberate pace, but is still comfortably Pub. It could trend the other way, if the Pubs tire of their infatuation with nationalist populism and fear of people not like themselves, but that is not likely to happen until the current Pub coalition ceases to be competitive, thereby forcing a course correction.
The giveaway is the German heavy suburban theme. I also wondered whether the chic burbs were the inner or outer ones. In Waukesha, they are the inner ones. That means Dem trending. If the reverse, that would probably not be the case.
I don't have a county in mind. A place that describes a place like Rockland or Orange in NY would be interesting with disparate cohorts of voters trending in disparate ways, with different growth patterns.
