Greetings Gary and Kay:
Unfortunately, like 90%+ off all the tree health problems I receive via this Internet venue -- my answer is that you are going to need to contact a local professional forester, horticulturist, or arborist for an on-site assessment.
Without physically seeing the tree and knowing more about the general environmental conditions, it is extremely difficult, if not impossible, for me to provide you with a legitimate and valid recommendation. Furthermore, do not apply pesticides to your tree if you cannot identify the cause of decline.
Therefore, please contact a local professional forester, horticulturist, or arborist for an on-site assessment of your tree(s). In Illinois, please utilize the Illinois Arborist Association Website to help you locate a local, certified arborist:
http://www.illinoisarborist.org/CertifiedArboristsNew.htm
Best of luck!