G'day realdow.
As I believe you are coming into summer and your tree's are shredding. I believe rather then try to explain my answer to you, you could perhaps read about it in this link i'm going to provide you with, on deciduous trees.
http://en.wikipedia.org/wiki/Deciduous
With deciduous trees, the ones that are deciduous in the summer are usually tropical in tropic areas. I'm not to sure on the climate in Illonois, but if they didn't shed last year then they may be under alot of stress?
If you could post pictures (Including of a familiar object next to them so we can get a rough idea of the size) of your tree's and their spec's that would be of great help.