the Dresden Files-Twin Cities
Mortal groups encompass everything from secret societies like Freemasons and venitori, to religious sects, to political parties, to organized crime, to local gatherings of magical practitioners, to law enforcement. They run the gamut from being completely clueless about the supernatural, to knowing when the Merlin of the White Council scratches his nose.
Normal mortal authorities are present and active. If you tangle with a renagade sorcerer and kill him, you may find yourself in trouble with the law. Break into a building during the course of an investigation, try not to leave forensic evidence behind. Burn down a building with an errant spell…you get the picture. Most mortal authorities are completely unaware of the supernatural world, and will respond to your tales of Vampires or evil wizards by locking you in a rubber room with a comfy new jacket and lots of meds. Most major cities have a division of their police force, or at least a few individuals, who are at least vaguely aware of the supernatural, and either officially or unofficially deal with the “weird” cases. Such people can be an invaluable help in dealing with the mundane side of problems that crop up in your adventures. (Hint hint, nudge nudge, wink wink)