In order to produce the accurate information necessary for local taxation the Tenement Act of 1842 provided a uniform valuation of all property in Ireland. It was based on the productive capacity of land and the potential rent of buildings.

The man appointed Commissioner of Valuation was Richard Griffith, a Dublin geologist, and the results of his great survey, the Primary Valuation of Ireland, were published county by county between 1848 and 1864.

The Valuation is arranged by county, barony, poor law union, civil parish and townland, and lists every landholder and householder in Ireland. Apart from townland address and householder's name, the particulars given are:

The only directly useful family information supplied is in areas where a surname was particularly common. The surveyors often adopted the Gaelic practice of using the father's first name to distinguish between individuals of the same name, so that John Reilly (James) is the son of James, while John Reilly (Michael) is the son of Michael. Copies of the Valuation are widely available in major libraries and record offices, both on microfiche and in their original published form.

The Valuation was never intended as a census substitute, and if the 1851 census had survived, it would have little genealogical significance. As things stand, however, it gives the only detailed guide to where in Ireland people lived in the mid-19th century and what property they possessed. In addition, because the Valuation entries were subsequently revised at regular intervals, it is often possible to trace living descendants of those originally listed by Griffith.

A complete index of Griffiths Valuation can be found at the Clare library.