An interesting resource for this might be a (new?) RPG called Colonial Gothic which uses the notion that there are supernatural nasties in the 1776 era.
If you're looking for something set in colonial America using supernatural, try Witchhunter from
Paradigm Concepts. The system is relatively easy to learn, the setting is rich and well developed with lots of secret organizations and incorporates the "real world" of late 17th century western civilization very well. They also have a world wide campaign that runs at gaming cons called
Dark Providence.
----------------------------------------------------------------
A campaign I thought would be interesting is early age of enlightenment:
Hello, allow me to introduce my self. My name is Charles Whycross, I'm an apothecary in London. I'm part of a dying breed, because I'm also a wizard. It's funny in a way that I should make my living in what is so obviously a "magician's" profession. I say it's funny, because not so many years ago I lost a lot of people who might have been wizards and witches and warlocks. Between the publication of "The Witch's Hammer" and the Inquisition I've lost most of my family and friends. Even those I still have don't see much of each other. We're scared to be seen together for fear that someone will think we're a gathering coven.
Things are getting better though. A few years ago, Isaac Newton published some papers on theories of motion and gravity. He kind of kicked off a movement. Nowadays they call it "The Enlightenment". Science, they say, can explain everything in the world: why things fall, how the body works, how to capture the power of nature. It seems popular, people like what it tells them. maybe in another hundred years or so, everybody will have forgotten about magic and wizards and consorting with the devil. Of course, that's also the problem.
You see, part of the strength of magic is belief. If everybody believes in magic, it's more potent, it's everywhere. If people stop beleiving though, the fabric of magic will weaken. Sure, it'll never go away completely. There will still be things that go bump in the night, and places of power. After all, it's not like we won't have fire and wind and water, but the air won't buzz with magic anymore. The White Council tells me I don't know what I'm talking about, that magic is elemental and ever-powerful. But I see it, I feel it in my fingers, I sense it in the fey I deal with on occasion: the magic is weaker than it used to be.
Who knows, maybe I'm just getting old and cynical, maybe I need new scenery. I suppose I could always go to France and see if the new king needs a court philosopher. It worked out pretty well for Nostradamus, and the air in France is a lot cleaner than it is here in London.