Cleveland makes its cassata cake with whipped cream, strawberry and vanilla custard.
Didn’t realize until recently that the rest of the world, if they make cassata cake at all, is made with ricotta cheese, candied fruit and chocolate cream.
Cincinnati!
The chili (love/hate for most), Skyline is my favorite, I think Gold Star tastes like eating a pine tree.
Goetta, especially from Gliers…goetta everything…goetta omelets, pizza, etc.
Brats/Metts, although they are everywhere now.
Graeter’s Ice Cream, some of the best in the world, particularly black raspberry chip.
Montgomery Inn Ribs…I personally don’t like them but they have a huge following.
I feel I am missing something…but these are the foremost, with “Cincinnati Chili” being chief among them.
3 for $1 bags of Cheetos-like product. 
Not so much the food, but the deals…
I think the others have Chicago covered, so I’ll mention that I grew up in Peoria, which is on the northern edge of horseshoe territory. I didn’t even realize they were a local thing until a couple years ago when I heard someone talking about how they had an “Illinois Horseshoe.”
I was going to take exception to your claim for pasties but I was thinking of the Iron Range, which has a lot of foods in common with the U.P., including porketta and klobasa (not kielbasa). Oh, and Rangers and some Pittsburgh locals are the only ones I know who also make potica. I used to make it but then I was declared a celiac and had to lay off the wheat.
Burgers with large pats of butter on them (yeah, we’re healthy Cheeseheads), Beer Brats, Frybread.
Central Illinois has horse shoes, I don’t know if they’re popular anywhere else.
Dekalb Illinois is known for its beer nuggets.
I believe pasties originated in Cornwall (at least by that name - the idea of putting a meat filling into a baked crust probably originated in Sumeria) so pasties are presumably local cuisine any place where Cornishmen (Cornwallers?) settled.
The Oostburger, a sandwich containing a hamburger patty and a bratwurst on a Sheboygan-style hard roll, seems to have come from the village of Oostburg, Wisconsin.
Here in Sacramento we have the Merlino’s Freeze. Think Slurpee, but made from orange juice, water, and sugar. The perfect summertime treat.
I give you the Sonoran hot dog.
I know I had it back in the 80s and I’m sure it has been around longer than that.
In almost all of the country, chili is a term for a stew like offering of beef, onions, tomatos of some preparation, often but not always with beans, and some sort of chilies for heat and flavor.
In Colorado, New Mexico, and Utah, if you go into a restaurant ahd just ask for “a bowl of chili” you are almost certain to get Chile Verde, a more soupy dish made from green Anaheim chiles, tomatillos, and pork (among other things.) It has nothing in common with what the rest of the country thinks of as chili. It can range from mild to blisteringly hot.
Although I haven’t had one, the Magic Mountain is a local food item.
First of all, and this is for everyone in this kind of thing. If you don’t have your location listed, you should probably mention it. Serenata, I gather you’re in Wisconsin…do they not have butter burgers elsewhere?
Also, I just found out recently that fish fries (as in “I’m going to get a Fish Fry later”…errr, that’s fried fish, not like french fries made with fish) are a midwest thing. Or at least aren’t nearly as big of deal once you get out of my area. In Milwaukee, it seems like everyone goes out for a fish fry on Friday. I know of at least one restaurant that has a line wrapped around the block at their drive though from about 4:30pm until they close.
No, a slurpee is much runnier than a Merlino’s freeze. It’s more like an Orange Julius only icier, no diary. A must have at every Sacramento River Cats game.
Well, the OP does say “relatively rare.” Many of the foods mentioned in this thread I could find around here if I want to, but I definitely think butterburgers are a Wisconsin thing, Culver’s locations in the Midwest and elsewhere notwithstanding. (However, I never thought of brats as being anything but ubiquitous, but that could be because I live in the Midwest. Not sure I’ve ever tried seeking out brats elsewhere.)
A very close friend of mine makes those at his Milwaukee restaurant…he’s going to be featured on Man Vs Food tomorrow (Wednesday). For a second, I actually thought that was one of the pictures I took that we sent in to the producer.