While I have never been there myself, I have heard the Mark Twain Museum in Hannibal is worth a visit.

Can't get much more American than Twain.

And my favorite Illinois state park is in the general area--Mississippi Palisades State Park. Of course, I haven't been there in decades, so it could well have been loved to death by now.

And Galena, Illinois used to be quaint and not very touristy, but that's probably gone done the tubes by now. "Progress" and all that.

My sister was once a huge Elvis fan, so enjoyed Graceland. I don't know if it is worshipped more by the cult folk or the kitcsch folk. Does that matter to you?