Data from the 2021 census released on Tuesday shows 15.9 per cent (1,068,268) of Australia's families had one-parent, having steadily increased from 1996 when the figure was 14.5 per cent.

Of the single-parent families, four out of five parents were female.

The census also showed the portion of couple families without children living in the same dwelling has risen to 47 per cent.

That's an increase from 1996, when 41 per cent of couple families didn't have children under the same roof.

There are more than 5.5 million couple families in Australia, with 53 per cent of those having a child living with them.

Some 46.5 per cent of Australians aged more than 15 years are in a registered marriage (9,665,708) in 2021, a drop from 2016, when 48.1 per cent were married.

Nearly 24,000 same-sex marriages have been recorded since laws changed in 2017. It equals 0.25 per cent of all unions.

Divorces continue to increase, with 1.8 million Australians aged more than 15 years divorced, up from 1.4 million in 2011 and 1.6 million in 2016.

More than one million people are widowed, and eight of 10 widowers are female.

Statistician David Gruen said the data showed a variety of families in Australia.

"The 2021 census data provides a fascinating glimpse into the structure and changing profile of Australian families.

Dr Gruen noted people aged over 55 years looking after another person's child had risen by 140,000 people at the 2016 Census, but then dropped by 50,000 at the 2021 count.

"There may be some COVID-19 impacts on child care arrangements, with the census seeing a reduction in people aged over 55 years looking after other people's children, for example their grandchildren."

Australian Associated Press