Census day is an official count of the Republic of Ireland's population on a specific date. The 1981 census took place on 5 April, ten years since the last full census.
Reporter Brendan O'Brien outlines how the census works. It is obligatory under law to give the information required and all information provided is strictly confidential.
The results provide data on the changing social and economic patterns since the previous census. Each household or institution must provide information on every person staying in that location on the night of the census. However, babies born after midnight will not be included.
The 1981 census includes some new innovations including an option to have any adult listed as the head of the household. Divorced people will fall under the "other" category for marital status.
Ticking boxes is also new this time.
Another new innovation on this year's census is box-ticking, which will facilitate coding and processing of data collected.
An RTÉ News report by Brendan O'Brien broadcast on 5 April 1981.