Every five years people in Australia complete a Census. A census is the official count of how many people there are in Australia.
This is the first time the census has been available to complete online. Officials had estimated that two thirds of Australians would fill out the census online this year, rather than on paper.
However, on Tuesday night the website crashed, preventing thousands of people around the country from completing the survey online. The Australian Bureau of Statistics is working to get it fixed.
People officially have until 23 September to complete the census online.
The first results from the census will be released in April.