The earliest and most complete census records for Ireland are for the years 1901 and 1911. Census returns from the 19th century were either destroyed by the government, or destroyed by a fire in the Public Records Office in Dublin (Four Courts) at the start of the Irish Civil War in 1922. For the period prior to 1901, family historians rely on census substitutes - records that list individuals living in a particular geographical area during a specific time period.