The first attempt at an official census, in 1813, was only a partial success. It was 1821 before a completed census was achieved. Thereafter decennial censuses were taken until 1911. Two interruptions to the decennial rhythm of population enumeration occurred: Partition and the Second World War. During this interim period, between 1921 and 1951, census taking was not forsaken, but disrupted in both the Irish Free State and Northern Ireland. This book focuses on the ten censuses from 1821 to 1911, with special attention being given to the 1841 and 1851 censuses. Three distinct areas are discussed - their provenance, the contents and how the census aids our understanding of the Irish economy and society in the past.