I'm in Plainfield. Anything south and west of me is open farmland with some good rollers and decent elevation changes considering you are in Illinois. Look at google maps the areas between Joliet/PLainfield/ Yorkville/ Morris and you will find fantastic roads to ride. Again, considering you are in Illinois.

You can also go to the recently opened Cal-Sag trail and that connects to the I&M Canal and Centennial trails. You can easily do a Century there with ZERO traffic by connecting those trails. Lots of services along the way.

Other then a nice leisure ride on the weekends or during business hours the Lake shore trail is a mess. Tourists, dog walkers and people not paying attention makes it impossible to carry a decent steady ride. Be prepared to stop lots and go slow n the busy areas. But on a nice sunny day its very pretty.