The name of the town existed before Superman was created.
Only because Illinois already happened to have a town called Metropolis when the comic books first came out. The IL legislature later voted to make it the "official home of Superman" for tourism purposes. There was no other already existing town called Metropolis in the US, as far as I'm aware...
The town it is in is called Metropolis. They made an agreement with DC Comics & it's been declared The Official Home of Superman. Extra fact: Superman's creators lived in Cleveland, OH when they came up with the character. I'd love to see a Superman museum there.
Illinois was the first to grab hold of the idea.
Thanks! Your answer is awaiting moderation.