The site explains that
The Civil Records of Births, Marriages and Deaths are the official State records of Births, Marriages and Deaths in Ireland. The registers of births, marriages and deaths and the related indexes are maintained by the Registrar General in the General Register Office. The Index books can be viewed at the General Register Office, Werburgh Street, Dublin 2.
The General Register Office (Oifig An Ard-Chláraitheora) is the central civil repository for records relating to births, stillbirths, deaths, marriages, civil partnerships and adoptions in Ireland.The Indexes to the Civil Records of Irish Births, Deaths and Marriages date from 1864 with non-Roman Catholic Marriages recorded from 1845. The indexes to Births over 100 years old, the indexes to Marriages over 75 years old and the indexes to Deaths over 50 years old.
Many of the records have been digitized and are available online.
Search the Irish Civil Records