I'm just a couple of hours south of Chicago, in Indiana. I'm starting to have the same problem as well. However, the best method I found for this is what many have mentioned on here. Get a big storage bin from Walmart. Put your carboys/fermenters inside it with a few inches of water. This has worked so far this season to lower the temp to around 68 for me. Once temps get hotter, you can have a few bottles of frozen water on hand and rotate them in and out of your storage bin. Once one melts, put it in the freezer and replace with a new one. Works pretty good for me.
Tiocfaidh Ar La
"I kissed the bottle, I shoulda been kissin' you"-jawbreaker