I have not lived out that way for more than a decade, but when I did, I helped clear parts of a perimeter trail at deer grove in palatine. Not extreme, but a good workout loop. I remember that the inner trails were very torn up and closed off - hence the outer loop revitalization.

I also one rode at waterfall glen which is somewhat near palos. I am not sure of the current status of those places.

Further south, I rode some pretty ok trails at Kickapoo just east of champaign urbana.

Working and riding with a local advocacy group will get you in on some local fun. You might also meet some people that would be willing to let you carpool out to some of the good stuff in WI or MI. I really liked the singletrack near wausau, WI at nine mile.

http://www.cambr.org/