When I was compiling a list of museums of illustration, I overlooked the Mazza Museum of International Art from Picturebooks.
It is located on the campus of the University of Findlay in northwest Ohio.
The five adjoining rooms display hundreds of original children’s book illustrations, drawn from a collection of approximately 3400 works. The collection has grown from just four original works purchased a little over 25 years ago.
Displayed beneath the originals are copies of the books for which the works were created, along with black binders with more information about each of the creators.
When I visited last week, they let me add to the Artist's Wall, right next to C.F. Payne.
The museum is free of charge, but accepts donations.
Wikipedia on Mazza.