The thing about the suburban counties around Detroit is that they have a lower median income than the collar counties around Chicago. DuPage and Lake are full of wealthier establishment Democrats who are more likely to vote for Clinton.
I know that anecdotal evidence should always be taken with a grain of salt, but if anyone knows the collar counties, it's muon:
Out in the western burbs of Chicago, Bernie signs are everywhere and there's nothing for Hillary. There's not really much of any Pub Pres candidates either and this is usually 60-40 Pub territory. It seems like every Dem house I know has a Bernie sign.
Signs do not vote and the "so and so has more signs out" theory has been debunked years ago. It's the same thing as with crowd size and people assuming big crowds means a big win.