Australians are increasingly unlikely to worship a god and more likely to come from immigrant families.
The 2021 census has revealed a growing nation — more than 25 million people — that is more diverse than ever.
It also depicts a country undergoing significant cultural changes.
For the first time, fewer than half of Australians identified as Christian, though Christianity remained the nation's most common religion (declared by 43.9 per cent of the population).
Meanwhile, the number of Australians who said they had no religion rose to 38.9 per cent (from 30.1 per cent in 2016).
The data also shows almost half of Australians had a parent born overseas, and more than a quarter were themselves born overseas.
LIVE UPDATES: Read our blog for the latest news on the 2021 census data
The census — a national household questionnaire carried out every five years — took place in August last year amid the worsening COVID-19 pandemic.
The nation's two largest cities, Sydney and Melbourne, were in lockdown and residents of regional New South Wales, Victoria and the ACT were about to join them.
Yet Australian Statistician David Gruen said the census was a success despite this challenge, with the household response rate rising to 96.1 per cent from 95.1 per cent five years earlier.
About four in five households submitted their answers online.
The Australian Bureau of Statistics (ABS) will begin publishing census results today and release more data in coming months.
The information helps governments improve their services, and helps researchers and businesses better understand the community.
Beliefs and family traditions are changing
Christianity was the stated religion of about 90 per cent of Australians until 1966, when its dominance began to wane.
The ABS says migration has affected the trends since, though much of the change is due to the growth of atheist and secular beliefs.
The fastest-growing religions, according to the latest census, are Hinduism (2.7 per cent of the population) and Islam (3.2 per cent), though these worshippers remain small minorities.
The 2021 census was also the first to collect data since same-sex marriages were allowed in Australia.
Almost 24,000 of these marriages were officially recorded.
However, marriage itself is becoming less prevalent.
A generation ago (in 1991), 56.1 per cent of Australians aged over 15 were in a registered marriage. That has now dropped to 46.5 per cent.
New Australians are increasingly from India
Australia has long been one of the world's great immigration nations, accepting more people than most other countries.
Last year, almost half of the population (48.2 per cent) were first or second-generation migrants, having at least one parent born overseas. That compares with 41.1 per cent 30 years ago.
Of the 27.6 per cent of Australians who were themselves born overseas, the most common country of birth was England.
However, India has become the second-most-common source country, overtaking China and New Zealand.
The census also asked Australians to report their "ancestry", as opposed to their country of birth or ethnicity.
The top responses were English (33 per cent), Australian (29.9 per cent), Irish (9.5 per cent) or Scottish (8.6 per cent), with another 5.5 per cent saying Chinese.
Census expands to consider illness and veterans
Last year's census was the first to collect information about Australians' long-term illnesses as well as the population's military service.
The most commonly reported chronic ailments were mental illness, arthritis and asthma.
The likelihood of Australians saying they had long-term sicknesses increased with age.
Women were also more likely to report a long-term health problem.
Among children younger than 15, asthma was the most common condition, affecting 7.4 per cent of boys and 5.3 per cent of girls.
Meanwhile, more than half a million Australians (581,139) told the ABS they had served, or were serving, in the Australian Defence Forces (ADF).
The vast majority were men (86.6 per cent). Most were former personnel (85.4 per cent) rather than actively serving.
The question about ADF service was included because of a dearth of information about veterans in the community.
Dr Gruen said the answers would be used, along with other government records, to help plan services for veterans.
The first release of census data will be published on the ABS website from 10am.
