Hmm... this is a hard one. Illinois has numerous counties I don't really care for, but don't really hate. I guess it'd have to be Morgan County. I hate its shape and I once got lost in "downtown" Jacksonville, so there. But outside Chicago, county lines really don't matter... it's all corn and soybeans.
Oh I also hate the shape of Tazewell County too.
You clearly haven't been around your own state much if you think it's "all corn and soybeans," but I highly doubt it's worth it to argue about this with you.
Anyway, the objectively worst county in Illinois is Alexander. That shouldn't even be debatable. It's hell on Earth.