Just adding on to what
@CGSwans and
@snowleopard have stated above. Let me reiterate that I have no issue with speculating what zoo(s) are next. With that said, I don't want the speculation to stifle discussion of the zoos actually being covered or the zoos that didn't make the cut, so I would appreciate it if we limited all of the guessing to an extent.
@birdsandbats lives in Wisconsin, the American capital of crappy roadside zoos. I assure you he is being completely serious.
That's a pretty bold claim calling roadside parks the most important type of American zoo. You'll be disappointed to find there aren't any on this list and quite frankly I don't see a place for them. There will be some controversial choices as well as some very niche facilities, but having roadside places represent America's must see zoos would be foolish.