What happens to all the census forms?
27 March 2011 Last updated at 09:18 BST
All the information that people write on their census forms is meant to relate to whoever is in their house on 27 March 2011.
But what happens to the information once the questionnaires have been filled in and sent off?
BBC News was given exclusive access to one of only two places where the forms are processed.
Rona Dougall reports.