It's absolutely true. Fact is, there are really only three counties in Illinois that determine all state wide and federal races because the bulk of the population lives in those three counties.
One is C(r)ook County, where Chicago is.
The second is East St. Louis
I don't remember the third (perhaps someone else may.) Unfortunately these three counties are also heavily DEMOCRAT, so the rest of us who don't live in these three counties are SCREWED by them, and our votes typically never count.