Greetings Cheryl,
Unfortunately, without detailed quality picture images and an on-site evaluation of your tree, it is extremely difficult for me to offer you any suggestions. Simply based on the above information, the "black" is probably compartmentalized wood or decay.
More often than not, as I have indicated many times throughout this forum, only an on-site evaluation by a tree care specialist (foresters, horticulturists, entomologists, pathologists, and certified arborists) can provide a legitimate diagnosis for tree health concerns. Even after an on-site evaluation is conducted, additional diagnostic procedures may be necessary – the University of Illinois Plant Clinic may prove useful in diagnosing certain diseases, insects, and plant injury http://plantclinic.cropsci.uiuc.edu/.
Therefore, please contact your local University of Illinois Extension office to determine whether they have anyone on staff (horticulturist or natural resources specialist) or whether they can refer you to someone who may be able to examine the affected trees. Moreover, you can always contact a local certified arborist to assist you http://www.treesaregood.org/findtreeservices/FindTreeCareService.aspx
Best of luck!
