I live southwest of Chicago, in LaSalle County, and I definitely think Chicagoans have an accent. And to me I do see traces of Wisconsin, not so much Minnesota. Even in places like northern LaSalle County I detect a bit of Wisconsin. The city of Mendota I say with a long "o". Some people from the area pronounce it MendOOta which sounds Wisconsin-ish to me.
Small observation, but I definately think some parts of northern Illinois
do not have that neutral accent that I am
positive I have.
I work with a woman who grew up her whole life 5 miles away from me and she sounds like she's from northern Wisconsin.
