My default no-planning route when I need a century starts on the LakeFront trail at Hyde Park where I live and, after ducking up some alleys above Loyola U., get to the Chicago/Evanston border. Once in Evanston, I take any of the long north-south streets just west of Sheridan until at some point I hit Lincoln then go Ashland north which finally takes me on a thoroughly bikeable Sheridan Rd. through Lake Forest and Lake Bluff. See
http://veloroutes.org/bikemaps/?route=1529 for a general idea. From Great Lakes, I head on back. Advantage here is, in event of disabling disaster, the Metra line is usually a short distance away.
From brotherdan: In Lake Forest there are local laws that prohibit bicycles on the streets. There is a bike path that runs along next to the road there. Both times that I came through Lake Forest I ignored the laws and stayed on the road. I would suggest doing the same, if only to piss off the pampered wealthy locals.
I've never had any trouble biking through Lake Forest--never noticed or heard of any no-bikng laws--and have found cops there pretty friendly and helpful including once dealing with a cranky motorist when those guys were great. Cops are ok generally along the North Shore. there are lots of bikers on Sheridan and they're all used to seeing them. Some may be seen to wave!
Although I am not of their exalted number, the pampered wealthy locals you mention have smiled to me and given a friendly word. One even deigned to assist me with a flat. ....those wealthy locals may reciprocate friendliness directed toward them. Maybe it's 'cause I don't view them with envy and cynicism. ---sorry to be a bit snippy here ;-)