I don't know about shore diving in CHicago, but Milwaukee is just a short drive to the north and there are a few wrecks that I could steer you to to dive on if you want.
I was out in Milwaukee last night freediving on a 258' freighter that went down in the 50's. Depths ranged from 60'-93' and vis was around 30'- last week vis was over 60'. We also have wrecks right off shore in 10'-25' of water that you could swim to.
Freedive-A-Palooza is the third weekend of July at Lake Wazee, about a 4-5 hour drive north of CHicago. We should have even more divers this year than last and your invited to come along if you want.
Another option, if your stuck in the Chicago area, is to just hook up on a local charter boat and go freediving on the wrecks just off Chicago. Most of them are only 30'-40' deep and the deepest one that I can think of, in that area, is less than 60'. You need to go north, to Wisconsin, to start hitting deeper depths, or take a 20 mile run straight out to dive the sub in 250', but people aren't giving those numbers up on that one too easily.
Water temps that time a year should be warm down there. We had 53 degree surface temps up here last night, but things warm up much quicker down there since the water is so much shallower. I would think a full 3mm would more than keep you warm. In early August around here we can usually dive in our swimsuits down to around 110' since the warm water starts to pool on one side of the lake or the other- depending upon the winds.
Here's a side scan image that my father-in-law did of the wreck we were out on last night. There are at least another 2 dozen wrecks in the area that we dive on a regula basis.
Jon