I don't know whether you guys have an equivalent thing, but over here we have the Office for National Statistics (ONS).
The ONS produce data on a variety of subjects, including statistics from the 10-yearly census we are required by law to answer.
The 2001 census was the first one to include a question regarding religion. That year, 390,000 people gave their religion as "Jedi Knight", making it the fourth-largest reported religion in the country.
I think they changed the question for the 2011 census Here are some statistics from my little corner of England from 2011.
NB the population of Wycombe as a whole is ~120,000.