Wow. Just... wow! As someone who grew up in Michigan and who tries to get back nearly every summer to the beautiful lakes and trees of that state, my mind is boggled! How in the world can anyone visit all 49 of the other states and miss this gem?
I hope you decide to leave about 3 days earlier and tour Michigan. You'll skip the horrible Chicago traffic by driving up the Lake Michigan side, over the mighty Mackinaw Bridge, and through the Upper Peninsula. Many great sights to see along the way. Then follow US 2 westward!
(edit: I've assumed you are doing this in summer weather. If you are contemplating an imminent departure, forget what I said... Michigan is probably just white right now.)