Two twentieth-century census returns are available for research and, in some measure, make up for the loss of the earlier records. Data was arranged by county, district electoral division, and townland, and absentees were not recorded. Most source guides caution genealogists against accepting recorded ages in the 1901 census because there is evidence from comparisons with the 1911 enumeration that many responses were too low. Under ideal circumstances any search in these twentieth century returns can be made knowing the street or townland of the ancestor's residence. Even when there is no alternative to a search through one or more films, the job will be easier if the district electoral divisions and townlands have been identified.
Several aids make it easier to locate the appropriate divisions.
The first are the townland indexes. District electoral divisions appear in the 1871 and 1901 listings but not in 1851. There is no townland index for 1911 but differences from the 1901 census are minor. Nominal indexes exist for the 1901 census of Longford, Fermanagh, and Tyrone, with Donegal to follow soon. For many names, genealogists have extracted all the entries and generally arranged the lists by county.