AUSTRALIANS with no religion are among the fastest growing population groups and their number is expected to increase in this year's census.

The Atheist Foundation of Australia has launched a campaign urging people with no religious affiliations to tick the ''no religion'' box on their census form next month.

Atheists are being urged to tick the "no religion" box in next month's census.

Billboards featuring the campaign have been erected around NSW, with a prominent one on busy Parramatta Road at Annandale.

David Nicholls, president of the foundation, said he expected a higher uptake of the no religion option this year. ''People are leaving traditional religion in droves,'' he said. ''I think that will become clear in the census this time around.''