I am in MN as well, northeast of the Twin Cities about 35 miles. The heat & humidity have been terrible, but the egg production has only dropped slightly. We'll see - Today may be the worst.
What I find with stress that causes drops in egg production, is that it doesn't start back up immediately after the stress factors go away. Meaning, when it once again becomes cooler & less humid, it seems to take a while for the shock on their bodies to drop off so they can start producing again.
I try not to give them as much scratch when it's hot, as corn has a high caloric content, which I think can increase their body temps. Lettuce, leftover fruit pieces, etc., seem to do better.