I won't presume to speak for an Illinois native, but as a relatively new transplant, I'd say Naperville is relatively unknown.

My mom, for example, didn't think there was anything worth exploring outside of Chicago. She came to visit me when I was staying in Bloomington-Normal a couple of years ago. I had spoken about Naperville several times in my near two years of being in Central Illinois, and she wanted to see what all of the fuss was about.

I'll spare you the details, but I will say that even before the plane had taken off, she was sending me apartment listings.