Subject: Mystery bug
Geographic location of the bug: Northern Illinois
Time: 05:16 PM EDT
Your letter to the bugman: What type of bug is this?
How you want your letter signed: Kate
This is a newly eclosed (just emerged from the pupa) Giant Silkmoth in the family Saturniidae, and its wings have not yet fully expanded. The antennae indicates it is a female. Of the species represented on the Illinois Department of Natural Resources site, it looks most like a Polyphemus Moth. The TYWKIWDBI site has images to support that identification. The Polyphemus Moth has very impressive eyespots on the underwings (not visible in your image) that are used to frighten predators.
Thank you so much! I did take another look 15 minutes later and the wings had grown with large dots just as you described. Your time is greatly appreciated.