Second-generation Australians will soon be in a minority.
The census shows Australia reached a "tipping point" in 2016 where only slightly more than half its residents had two Australian-born parents.
The long-term low of 50.7 per cent is a step down from 54 per cent in 2011 and 57 per cent in 2006.
More than a quarter of Australia's population was born overseas in 2016 (26.3 per cent, up from 24.6 per cent) and for the first time most of the overseas-born came from Asia rather than Europe.
China, India, the Philippines, Vietnam and Malaysia now account for more foreign-born residents than the traditional birthplaces of England, New Zealand and mainland Europe.
Two point two per cent of the population had been born in China in 2016, up from 1.5 per cent in 2011.
Asian immigrants are typically much younger than European immigrants, meaning that the switch to Asian immigrants is helping slow down the aging of the population.
The median age climbed from 37 to 38 between 2011 and 2016. One in six Australians is aged 65 or over.
The Bureau of Statistics counted 23.4 million Australian residents on August 9, 2016, up 1.9 million from 2011.
Adjusting the total for an estimated 1 per cent undercount and 600,000 Australians travelling overseas, the Bureau believes Australia's population was 24.4 million on December 31, around 100,000 more than it had thought.
Melbourne is gaining on Sydney for the title of Australia's biggest population centre, growing by 12.1 per cent to 4.485 million since the previous census, compared with Sydney which grew 9.8 per cent to 4.823 million.
Darwin was Australia's fastest-growing capital city, growing by 13.5 per cent, followed by Perth which grew by 12.5 per cent.
More than one quarter of the population was born overseas in 2016.
Two-thirds of all Australians live in capital cities, and 86 per cent of migrants.
Migrants make up 28 per cent of the populations of NSW and Victoria and 32 per cent of the population of Western Australia.
They make up only 12 per cent of the population of Tasmania.
While English remains Australia's most-used language, it is becoming less common, with 72.7 per cent of residents reporting they spoke only English at home, down from 76.8 per cent in 2011.
Mandarin is spoken by 2.2 per cent of Australians, up from 1.6 per cent, and Arabic by 1.4 per, up from 1.3 per cent. One point two per cent of Australians speak Vietnamese, and another 1.2 per cent Cantonese.
The Census recorded 300 different languages, including indigenous languages.
A record 2.8 per cent of Australians identified themselves as Aboriginal or Torres Strait Islander, up from 2.5 per cent in 2011 and 2.3 per cent in 2006.
Although the census has been conducted every five years since 1911, it has only been mandatory to count indigenous Australians since 1967.