Here are several easy ways help you identify your tree:
1. Take a leaf, twig, and fruit sample to you local Illinois Extension Office.
2. Take several high-resolution photos of the tree's bark, leaves, twigs, and fruit -- email them to email@example.com
3. Utilize a quality internet site (e.g., http://www.cnr.vt.edu/DENDRO/DENDROLOGY/factsheets.cfm)
I'm not sure what you mean by registered? Are you speaking of the Illinois Big Tree Register? If so, please visit the online version of the Illinois Big Tree Register:
Best of luck!