I live a couple hours south of ya and I've walked thru the starved rock area a few times. I have only found a few small pieces there but, I'm confident there's some good stuff. If you can take a trip to the western side of the state you will have better luck looking in the creeks. Since the Mississippi River valley tends to have a plethora of knapable rocks.
Good luck with the rock hunting, and let us know how it goes.