On the 2011 census (it takes places every five years) 64,390 Australians put "Jedi" down as their religion, an increase of from 58,053 on the 2006 census, according to The Brisbane Times. Numbers like that put "Jedi" right behind Sikh on the list of religions in the country. It seems unlikely that all these people truly believe themselves to be actual Jedi, and most of them make the claim as a harmless way to declare their Star Wars fandom and give the government the middle finger at the same time.
However, a group called the Atheist Foundation of Australia is leading a campaign to get people to stop making this joke. Their reasoning is, that when officially counted, Jedi gets classified as a "Not Defined" religion instead of "No Religion." When that happens, they believe "it makes Australia seem more religious than it really is." Which, again, doesn't sound like a problem, but "data on religious affiliation is used for public policy, city planning, community support facilities and more.