Were there really 1 million unoccupied dwellings in Australia on census night 2021?

Background 
The 2021 Census in Australia revealed that just over 1 million dwellings were ‘unoccupied’ on census night. This finding was widely reported and may have given the impression of a large number of vacant dwellings ready for households to move into, potentially offering a solution to homelessness and those struggling to find suitable or affordable accommodation. 
Aims 
The aim of the paper is to investigate whether there really were 1 million unoccupied dwellings in Australia in 2021, to shed some conceptual and empirical light on exactly what is meant by an ‘occupied’ and an ‘unoccupied’ dwelling, and also try to understand why dwellings were unoccupied. 
Data and methods 
We used a variety of census, population, and dwelling data to estimate the number of private dwellings disaggregated by occupancy on both a de facto basis (whether people were present in dwelling on census night or not) and on a usual residence basis (whether people are usually resident in a dwelling or not). A comparison with the situation at the time of the 2016 Census is made. 
Results 
The results show that there were indeed about 1 million dwellings unoccupied on a usual residence basis in Australia in 2021. But they were not the exact same 1 million unoccupied on census night, and not all of these dwellings were available to households to live in. There was a substantial increase in the number of dwellings unoccupied by usual residents between 2016 and 2021; we suggest some possible reasons for this, including Covid-related effects. 
Conclusions 
Greater clarity and more detail are needed in census dwelling data. In addition, it would be useful if there were detailed annual official statistics on dwellings and households to better inform housing policy and research.