Re: Archenemy
Chicago has a lot of Irish influence, especially when it comes to politics. I don't know if you have ever heard of the "Daley machine" that was controlled by mostly Irish politicians and their mafia connections. Chicago also dyes the river green for St. Patrick's day and has a huge parade (it used to have two).
I agree keeping it a secret would be better story-wise since having them out in the open would have too much of an effect on the world. It's far too easy to get bogged down in the details of world building and lose sight of the story. Once you start getting into how weretigers impacted the British colonial system in India or werewolves influence on the Protestant Reformation you'll forget about character driven stories.