As I mentioned before, it looked like one of things White wanted to do was a catalogue of monsters unique to Americana. He seemed to mostly draw from folklore and cryptozoology. The task can be pretty challenging for the same reason it had to be done--most United States culture post-dates a common belief in the supernatural. I theorize that, as a largely European-based culture, there's probably a lot of European creatures like dragons, elves and goblins. However, the point here is to explore the quintessentially American ones.
On the original map, White only has five; The Mothman, Bigfoot, the Jersey Devil, some kind of representation of Aliens, and the Jackelope. The Jackelope has already been featured on the Herdsmen page. Bigfoot would be on the Pacific Northwest one, (Maybe the district of Columbia in particular) the Jersey Devil in New Jersey (natch--maybe the motivator in making it its own nation), the little Roswell fellow would probably be on the New Mexico page. The Mothman could be part of the Piedmont page, but it's not out of the question for it to be in Ohio. Somewhere in the Appalachian range. Maybe even the "East Heresy" or "Tennessy" page.
For me, five was too few though, and I added four more of the Jack O'Lanterns. I could have added many more, but that might have crowded up the feudal core a little too much. I wanted to spread it out a bit. But two monsters that have existed in folklore are the Squonk and the Goatman. The Squonk is said be an ugly, warty creature that sheds tears when captured, dissolving itself in self-pity and shame. The Goatman is an Satyr-like creature that attacks dogs and parked cars. Similar creatures are also said to inhabit Colorado and Kentucky. However, I wouldn't know where to put it. Not only does the Mid-Atlantic have its own beast, but Maryland, as an entity, no longer exist. Plus, less cars for it to attack.
Near the great lakes, one could talk about the hodag, another denizen of lumberjack myth, like the jackelope. A strange cross between a dragon and a rhino, they are said to inhabit Wisconsin and Minnesota. Legend has it, their legs cannot bend, so they sleep leaning against trees. Chopping down its sleeping tree will make it an easy capture.
Upper Quebec would be a great place to talk about the Wendigo, the most well-known of Native American monsters. Obviously, not a lot of American Indian myths would be subject to this kind of thing, (Their folklore is heavily guarded and taken very seriously) but the Wendigo has nontheless been a very frequent opponent in popular culture, throughout films, novels and comic books. It would also add a bit of spice to the Quebec page.
The next two, I'm not dead-set certain on. I have an icon placed on the gulf coast, because the gulf has always been treated as a ripe place setting for the supernatural. New Orealns itself is too "tame" for a mythical beast, but something may be out there in the bayous. Perhaps the best choice would be the "Loupgarou"--Louisiana's answer to the werewolf. Florida also has reports of a bigfoot type creature, the "Skunk Ape". Alabama is also home to the "Wampus Cat", a felinoid shape-shifter. In any case, these, or a combination thereof, could be great monsters.
And finally I have an icon for Death Valley. As you can see, there should be a pattern of "Here be monsters" in rather remote locales. The first one that comes to mind is the Chupacabra, the most famous modern monster in Latin America. However, between the Jackelope's page, and the possibility for the "Roswell" monster, it might be a little redundant. However, upper Mexico has many possibilities, like the weeping La Llarona, and the fiery El Zobro.