I wouldn't worry too much about the premature leaf drop, assuming these trees were fine all summer. After all, it is September 12 and we've been pretty darn dry the past 4-5 weeks! Not to mention last year's excessive heat and drought -- trees are obviously going to be under stress!
However, you can always contact a certified arborist for an on-site evaluation of the tree/trees in question!
Illinois Arborist Association: http://illinoisarborist.org/services-we-provide/find-an-arborist/