The first successful census in Ireland was undertaken in 1821 and every 10 years thereafter.

The original census returns for 1821 to 1851 were largely destroyed in the Four Courts fire in 1922 (though fragments survived and are online at NAI-link).

The original returns for 1861 through to 1891 were destroyed prior to destruction of the PROI in 1922 (almost nothing survives).

Indexes to the Townlands, Towns, Parish, Barony, Poor Law Union and County were prepared from the census returns from 1851 through to 1901 and these are accessible below.

While the most commonly used indexes are to the 1851 and 1901 censuses, the others, including a couple of supplements are provided. And while there are many useful online indexes and guides to identifying townlands, the value of the alphabetical indexes of the original source can not be overstated.