The Composition Act (1823) specified that tithes due to the Established Church, the Church of Ireland, which had hitherto been payable in kind, should now be paid in money. As a result, it was necessary to carry out a valuation of the entire country, civil parish by civil parish, to determine how much would be payable by each landholder. This was done over the ensuing fifteen years, up to the suspension of tithe payments in 1838. Not surprisingly, those who were not members of the Church of Ireland fiercely resented tithes, all the more so because the tax was not payable on all land; the exemptions produced spectacular inequalities. In parts of Munster, for instance, tithes were payable on potato patches but not on grassland, with the result that the poorest had to pay most. The exemptions also mean that the Tithe Books are not comprehensive. Apart from the fact that they omit entirely anyone not in occupation of land, certain categories of land, varying from area to area, are simply passed over in silence. They are emphatically not a full list of householders. Nonetheless, they do constitute the only countrywide survey for the period, and are valuable precisely because the heaviest burden of tithes fell on the poorest, for whom few other records survive.
From a genealogical point of view, the information recorded in the Tithe Books is quite basic, consisting typically of townland name, landholder's name, area of land and tithes payable. In addition, many books also record the landlord's name and an assessment of the economic productivity of the land. The tax was based on the average price of wheat and oats over the seven years up to 1823, and it was levied at a different rate according to the quality of the land.
Microfilm copies of the Tithe Books for the twenty-six counties of the Republic are available in NAI, NLI and via the LDS Family History Library, with the exception of parishes alphabetically between 'Drung' and 'Duncormick'. This sequence was overlooked by the LDS microfilm team. Images of the other parishes and a database transcript of personal names and placenames is available at genealogy.nationalarchives.ie and at FamilySearch.org. The transcript is deeply flawed, with a myriad of transcription errors and widespread mis-identification of parishes. The best that can be said of it is that it provides online access to the images to allow searching by hand. The FamilySearch copy is easiest to navigate. Shane Wilson (swilson.info) is engaged in disentangling some of the geographical mistakes. Ancestry.com has a better transcript of the same set of microfilms (dbid 1270), but without record images. The Tithe Books for the six counties of Northern Ireland are in PRONI and are available on self-service microfilm in the 'MIC15A' series. An index to the PRONI records is also on microfilm (ref MIC/15K) No images are available online, but transcript indexes are available for all six counties on the subscription site rootsireland.ie. The surnames in the Tithe Books have been roughly indexed for the thirty-two counties in the NLI 'Index of Surnames'.
The usefulness of the Tithe Books can vary enormously, depending on the nature of the research. As only a name is given, with no indication of family relationships, any conclusions drawn are inevitably somewhat speculative. However, for parishes where registers do not begin until after 1850 they are often the only surviving written records. They can provide valuable circumstantial evidence, especially where a holding passed from father to son in the period between the Tithe Survey and Griffith's Valuation.
An organised campaign of resistance to the payment of tithes, the so-called Tithe War, culminated in 1831 in large-scale refusals to pay the tax. To apply for compensation for the resultant loss of income, local Church of Ireland clergymen were required to produce lists of those liable for tithes who had not paid, the 'tithe defaulters'. The lists can provide a fuller picture of tithe-payers than the original Tithe Book and can be useful for cross-checking against it, especially if it dates from before 1831. Of these lists 127 survive, in the nai Chief Secretary's Office, Official Papers series. They relate principally to Cos. Kilkenny and Tipperary, with some coverage also of Cos. Carlow, Cork, Kerry, Laois, Limerick, Louth, Meath, Offaly, Waterford and Wexford. A full list was published in The Irish Genealogist, Vol. 8, No. 1, 1990. County-by-county microfiche indexes have been produced by Data Tree Publishing. These are available at NLI. An online version is available at FindMyPAst.ie.