Tracking down your Irish ancestors can be difficult, given the devastating loss of the 1821 through 1851 census returns in the 1922 Dublin Four Courts fire. Fortunately, Griffith's Valuation of Rateable Property (commonly called "Griffith's Primary Valuation") can act as a "census substitute." Published between 1847 and 1864, Griffith's Valuation is not only the first systematic valuation of property holdings in Ireland, but also the most important resource for locating mid-19th-century Irish residents. Now, you can access a fully indexed online version through a subscription to Irish Origins <www.irishorigins.com>.

Though not the first online version of Griffith's Valuation, Irish Origins' database is easy to search and lets you view digital images of the original volumes, including revisions and amendments. The database — produced by Origins.net in partnership with Irish genealogical publisher Eneclann <www.eneclann.ie> and the National Library of Ireland <www.nli.ie>- includes more than 1 million names of landowners, landlords and renters.

You can search all Irish Origins' databases at once, but if you search just Griffith's Valuation, you have more options to refine your search. A basic search lets you scan records by landowner, renter or place (including villages and street names). Using the advanced search, you can limit the results by administrative divisions such as county, barony, union and townland.