Australia's population has topped 21.5 million, according to the 2011 census results, although there has been a further decline in the proportion of people holding Australian citizenship.

The initial census results give a glimpse into the changing face of Australia, including its multicultural background.

The data shows one in four people were born overseas, and 15 per cent of the population does not hold citizenship.

Just under 70 per cent of the population was born in Australia - a further reduction since the previous census.

"Historically, the majority of migration has come from Europe, however, there are increasingly more people born in Asia and other parts of the world now calling Australia home," 2011 census executive director Andrew Henderson said.

"The leading birthplace for those who arrived since 2006 was India (13.1 per cent), closely followed by the United Kingdom (12.1 per cent)."

The data also reveals a dramatic increase (up 20.5 per cent) in the proportion of Australians identifying as Aboriginal and Torres Strait Islander since the 2006 census - with a third now living in capital city areas.

The Indigenous and Torres Strait Islander population stands at just under 550,000.

Census 2011 key points: 20.5pc increase in people identifying as Indigenous

20.5pc increase in people identifying as Indigenous Hinduism the fastest growing religion

Hinduism the fastest growing religion One in four Australians is born overseas

One in four Australians is born overseas Population has jumped by more than 17 million in 100 years

Population has jumped by more than 17 million in 100 years Median national weekly rents up by 49.2 per cent

Median national weekly rents up by 49.2 per cent 1,338 same-sex couples identify as married

The Australian Bureau of Statistics found the median age of the Aboriginal and Torres Strait Islander population is 21 years - 16 years lower than the national figure.

Growing Pains

Australia's population has risen by 8.3 per cent since the 2006 census, with the fastest growth in the resource-rich states.

Western Australia's population jumped by 14 per cent to 2.24 million people, while Queensland's grew by 11 per cent to just over 4.3 million people.

The states that recorded the lowest population growth were Tasmania (up 4 per cent), South Australia (up 5.4 per cent) and New South Wales (up by 5.6 per cent).

At a local government level, East Pilbara in Western Australia recorded the highest proportionate growth, with its population increasing by 82.6 per cent to 11,950.

Processing your data: 11 high-end scanners capable of scanning 130 pages per minute

11 high-end scanners capable of scanning 130 pages per minute Scanners operated five days per week from September to December

Scanners operated five days per week from September to December Approximately 9 million forms or 46 million pages were scanned

Approximately 9 million forms or 46 million pages were scanned 27,000 collector workloads including 500 from Indigenous remote communities

27,000 collector workloads including 500 from Indigenous remote communities All Census forms are destroyed after processing

All Census forms are destroyed after processing All scanned form images are deleted after processing Source: ABS

Brisbane recorded the largest jump in the number of people in a particular local government area - with its population topping 1 million for the first time.

At Home

Hinduism is the fastest growing religion, but most people still call themselves Christian, although the figure has dropped from 64 per cent in 2006 to 61 per cent last year.

According to the census, the proportion of people who reported no religious affiliation has increased from 18.7 per cent in the 2006 census to 22.3 per cent last year.

That group has now eclipsed Anglicans (17.1 per cent), while just over a quarter of the population identify themselves as Catholic.

The structure of families is also changing. The proportion of the population who are married has fallen, while those who have never married or are separated has risen.

Mandarin is now the second most common language spoken at home other than English, according to the census, taking over the spot from Italian.

The census has also revealed a significant jump in housing costs over the past five years.

Median weekly rent has increased by almost 50 per cent to $285 per week, and there has been a 38 per cent jump in median monthly mortgage repayments to $1,800.

The increase in the cost of housing has not been matched by household income.

The data shows median weekly income has risen by just over 20 per cent since 2006, to $1,234 per household.