As censuses have been compiled at different times under the direction of various offices, including Census Commissioners and the Office of the Registrar General, it is convenient to group these records together at this point. The first national census was taken in 1813, but was never properly completed and few returns survived before 1922. Thereafter censuses were compiled at ten-yearly intervals from 1821-1911, while the first census of the independent Irish State was taken in 1926. The census returns of 1861-91 were disposed of by Government orders before 1922 and all but fragments and abstracts of those for 1821-51 were destroyed in 1922. In addition, the National Archives holds a Census of the Diocese of Elphin 1749, and some copies of returns of the destroyed Religious Census of 1766.

The censuses of 1901 and 1911 for the 32 counties of Ireland, and surviving pre-1901 fragments, are open for public inspection in the National Archives (censuses from 1926 onwards are still closed). Microfilm copies of the 1901 census are available in the Public Record Office of Northern Ireland, county libraries and some other repositories in Ireland and abroad, and work is in progress to microfilm the 1911 census.