Urantia is a religion. The "sacred" text for this religion is the Urantia Book. It can be found in virtually any major bookstore in the "New Age" section. I'll have to do more research on this religion. I've looked into a bit in the past, because someone who is close to me is an Urantian.
Here's one site if you are interested in knowing more about this religion, however, this site refers to Urantia as a cult: http://withchrist.org/urantia.htm.
I think this group is growing and that they're doing so under the radar of publicity and doing so on purpose. Once they are fully established all over the world with great numbers, they will then go public.