Mayo Clinic in Rochester Minnesota is a very nice place to go for a diagnosis. I've been there several times for my husband and for myself, but you are right - there is no real reason to go there for a PD diagnosis. There must be several movement disorder specialists in Chicago. The Univ. of Chicago has a hospital and medical center, and I think Northwestern does too.
I suppose Mayo Clinic just comes to mind as THE place to find specialists when you live in the Midwest.
If you are not happy with the specialists you see in Chicago you can always go to Mayo for a second opinion......