the thing is that, most of Runeterra doesnt seem to have developed religion. best examples i know are Bilgewater with the mother serpent and Zaun with the Gray/Grey Lady.
Shurima had a worship regarding the Sun Disk. but it wasnt really an entity.
Freljord had a worship regarding the Watchers, but they for the most part have forgotten them ever since, save for Lissandra and her tribe.
Icathia in the old lore was related to worshipping the Void, however, as far as the new lore is coming out it seems they were actually fighting it or caused the void war.
Targonian society worshiped their own gods and they actually remain, just that only a few mortals are able to see them.
,
,
and
are avatars or heralds of some of the Targonian Gods.
Ionia is more about eastern spiritism and philosophy so they dont really worship gods, instead they have philosophical schools and spiritual rites related to illumination.
Noxus and Demacia seem atheistic, however, both the Noxian and Demacian ideals could be seen as an object of worship. but they dont have gods.
Bandle city has an obsession with the "mothership", however this is still old lore and im not sure if Riot will change it in the future.
Piltover is a technocracy with an emphasis on commerce, they dont worship gods.
the ruined king could be taken as an object of worship in the Shadow Isles. however, the only thing closer to a cult there are the followers of
and 
apart from Nagakabouros and the Targonian Gods, there's not much deities to see in Runeterra.