Due to the Freljordian creation myths, I'm wondering if there are other demigods in different regions with similar ones.
Beyond Rammus in Shurima obviously.
Is Alistar a demigod from the plains before Noxus took over?
I like to think that the definition of a God/Demi-God is very interchangeable depending on where you are in Runeterra.
As already seen, Freljord has Ornn, Anivia, Volibear and probably others such as the mentioned Seal Sister In Shurima, we already have the various Ascended beings, as well as some Shuriman villages such as Taliyah's mentioning a Great Weaver that we haven't seen Bilgewater has Illaoi's faith of a most-likely real and very powerful Nagakabouros And even Demacia has mentioned "Gods" as in plural before I'm thinking that Janna may count though, a Zaun champion, and maybe even Zilean if he gets a VGU
There are others but I'm not sure. These 3 are ascended beings, pretty much what a demi-god/god is.
Ionia has Lee Sin, the god of free elo. Who, for 6 seasons, fought back the nerfs against the Devs despite all logic and reason.
Bandle City has the devil incarnate 
I don't think most places have similar gods. Rammus, for example, could probably be an ancient Ascended, older than any of the others that we've seen.
I'm pretty sure Alistar is just a Minotaur. We know Minotaur are a race that mingles with humans and such; in the Piltover map there's a snippet about Minotaur blacksmiths, with a small illustration as well.
Nasus- renekton-azir from shrima. taric- diana-leona- pantheon from taregon. Janna from zaun.
It's pretty interesting that we have a lot of Demigods that main theme is War: 
.
But other stuff, like Death or Desires (like in Tahm's theme) have only one representable entity
is kind of a demi god, she was blessed by the spider God in the Shadow Isles, he gives her immortality
Is also a fire elemental powerful spirit who hosts a human body
is a prophetess of Nagakaburos, a depths goddess, of indigenous people of the serpent Isles localized in Bilgewater
due to his lore, is now a powerful demi-god-Like prophet from the void, he sacrificed Kassadin's daughter for power
Is also kind of a demi-god, he is a poweful statue who protects Demacia from magic
He is a star forger, litteraly what a god could be
are what we can call, "Grim reaper", gods of death, i'm not really sure for them yet
is an ascended spirit
was blessed by the Moon, she is not completely human, and she is the last lunar follower (Lunari)
and 
are from another dimension, they are immortal in the lore, I always thought they were the goddesses of Good and Evil, and they fit this role well
Plus the lore mentions several goddesses like the Gray Lady and the veiled Lady From Piltover and Zaun
