A census is a count of the whole population. It also collects statistics on topics such as age, place of birth, occupation, ethnicity, housing, health, and marital status.

A census has been taken every ten years since 1801, except during the second World War. The next census will take place in 2011.

During a census, a form is delivered to every household in the country. This form asks for detailed information about each member of the household and must be completed by law. The information remains confidential and anonymous; it can only be released to the public after 100 years, when many people researching their family history find it very useful. General census information is used to identify population trends and to help planning.