Sydney now has more than 100 suburbs where at least half the population lives in a flat or apartment.

Topping the list for high-density living is Sydney Olympic Park, analysis of the 2016 census shows. In that relatively new suburb, 99.9 per cent of the population said they were in a flat or apartment on census night last August.

The next biggest share was in the central business district suburb of Sydney (99.4 per cent) followed by Haymarket (99.3 per cent).

There were 15 Sydney suburbs where 90 per cent or more of the residents lived in a flat or apartment.

A breakdown of census housing data provided to The Herald by the Bureau of Statistics shows the high-density trend has spread deep into Sydney suburbia.

In Wolli Creek, about 14 kilometres south-west of the CBD, 97.4 per cent of residents live in a flat or apartment. The census found only 32 detached homes in that neighbourhood. In Harris Park, a suburb 22 kilometres west of the CBD, 82.2 per cent of the population lives in a flat or apartment.

There are now 41 Sydney postcodes located more than 10 kilometres from the CBD which have 50 per cent or more of the population living in a flat or apartment. A dozen of those suburbs are more than 20 kilometres from the CBD including Narrabeen, Hornsby, Parramatta, Liverpool and Sutherland.

Social researcher Mark McCrindle said a growing share of Sydney families is opting to live in a high-rise building rather than move to a detached house when they have young children.

"Now there's a lot more support for young families in apartment living," he said.

"That final ceiling for denser urban living is being broken as parents raise their children through the schooling years in apartments. We've seen that in Europe, we've seen that in some parts of North American and we've certainly see it right across Asia but we haven't really seen it in Australia. So we are approaching new terrain there."

The 2016 census, released last month, found 42.1 per cent of all dwellings in Greater Sydney are now medium or high-density which includes flats, apartments, townhouses, semi-detached and terrace houses. That's up from 38.6 per cent at the last census in 2011.

The share of detached houses in Greater Sydney fell from 60.9 per cent of all dwellings to 56.9 per cent between 2011 and 2016.

The shift to higher-density living is being driven by a variety of factors including proximity to employment, changing lifestyle preferences and affordability.

A Reserve Bank research paper published last month said the median price of apartments is about 30 per cent cheaper than for detached houses, "in part because apartments are typically smaller but also because apartments use land more intensively".

Greater Sydney added 64,300 flats and apartments between 2011 and 2016 pushing their share of all the city's dwellings to a record 28.1 per cent.

About 70 per cent of dwellings constructed in Sydney last year were medium and high density.

"There's a very strong trend on and Sydney is leading the charge," McCrindle said.

Even so, many parts of the metropolitan area remain completely untouched by high density lifestyles. The 2016 census shows more than 250 Sydney suburbs have no residents at all living in a flat or apartment.