All the info I have states that clay soil is very DENSE and has VERY FEW air pockets to trap water. The Mid-west has some of the BEST farming soil in the country. I'd suspect that you have soil more like a loom, at least on the top. You may have a clay-like soil as you dig deeper but I'd be inclined to think you'd have to dig pretty deep.
I know, the Mid-west is a BIIIIG place. You could be anywhere, and soils do vary.