I'm not from Chicago, but a fellow hunter buddy of mine, from here in CA, goes to Chicago every year to visit in-laws. And he brings his detector when he goes. And found several parks where silver and IH's were child's play. Eg.: 5 to 7 IH's at a pop, with a smattering of silver, on any hunt he cared to do.
He had the impression that local hunters were simply not skilled at deep turf cherry picking. And that the hard-core guys tended to be "relic hunter" types , not turf hunters . For whatever reason, he was doing good in some of the Chicago parks. He honed in on the ones that were in upscale areas (not ghettos), yet surrounded by 1800's type neighborhoods
That was 15 + yrs. ago. He and I were going to make a dedicated trip JUST to park hunt for a week-straight, but ...... as of yet, still have never gotten around to it. Not sure if it's still easy pickens there or not.
Good luck !