Do you have to go to Chicago? It's awesome, don't get me wrong, but it puts you in a bad spot. That area of the country is the least interesting in my opinion (I would know because I grew up there), and it's a 10-15 hour drive to the more interesting parts of the country.
Especially since it sounds like you're interested in National Parks, I would fly into: Denver, San Francisco, or Seattle and start from there.