Contact your local extension office and see if they have anyone that can come take a look at the situation. Some offices send someone on a site visit and some don't provide that service. If not, see if you can get a copy of a list of certified arborists in your area.

You need someone to find out the exact cause of the decline. It may be weather related if you've had a drought like much of the east or it may be disease or other problems. But guessing is not the right way to go and without actual observation of the trees, any answer you get would be only a guess. Guessing about tree problems can end up being very expensive!