The Public Record Office of Northern Ireland (PRONI) in Belfast recently placed online “Valuation Revision Books”: www.proni.gov.uk/ This is a major source for documenting the taxation process for a particular parcel of ground within a townland. In other words, the search feature is geographical rather than name based. The scanned collection includes a fully searchable place name index to the approximately 3,900 volumes covering 1864-1933.
If you know the locality, especially the townland where your ancestors lived, then you can utilize that to narrow your search for a particular range of years. I use these revision books when I need to know what happened to a family residing on a certain piece of property. With the PRONI database, you can also search the land backward, say from your findings in the 1901 or 1911 censuses.
The scanned document images are in color making this very useful as the different changes are coded by the ink color of the pen corresponding to various years. This collection covers counties the Northern Ireland counties of Antrim, Armagh, Down, Fermanagh, Londonderry/Derry and Tyrone.
This collection has until this compiled database, has only been available in manuscript books at the PRONI. This alone makes this a major addition to the world of Irish history and genealogy. As you document changes in the tenure of a piece of property, you can extrapolate perhaps when someone died, immigrated, became too old to be responsible for the tax, or maybe was evicted. This clues you into other records. It also helps you to determine changes in the landlords so you can look for rents and leases from the estate papers.
I highly recommend this free database. It may open up new research avenues for you and provide valuable social history of a townland along the way.