Patio,
Yeah, that stuff looks like limestone. Looks way too chalky to me, but at least you're on the right path: limestone is where chert is found. There is some flint in southern ILL, though I've never been there and found it myself. Now if you go to Missouri, there is chert all over the damn place. Central Missouri on I-70 around Columbia has lots of chert. I've seen what appear to be large flint nodules still lodged in the limestone of roadcuts in that area. I've also seen large beds of chert wherever the highway cuts through a hill.
I would start looking in creek beds, and start tapping rocks. Flint will ring, sounding almost like porcelain. Non flint type rocks will give a dull thud. If you can't find any around your place, begin widening your search. The midwest has lots of flint when you get into the right areas, so I'd just start looking.