People of Irish Catholic ancestry will be able to trace their origins back almost 300 years online from Wednesday.

Taoiseach Enda Kenny and Minister for Arts, Heritage and the Gaeltacht Heather Humphreys will officially launch online the entire collection of Catholic parish register microfilms held by the National Library of Ireland (NLI).

Involved are more than 370,000 digital images of the microfilm reels on which the parish registers are recorded and which will be accessible free of charge.

These parish register records are considered the single most important source of information on Irish family history prior to the 1901 census. Dating from the 1740s to the 1880s, they cover 1,086 parishes throughout the island of Ireland, and consist primarily of baptismal and marriage records.

The NLI has been working to digitise the microfilms for more than three years under what is described as its most ambitious digitisation programme to date.

Ciara Kerrigan of the NLI said: “We . . . received a hugely enthusiastic response from people worldwide with an interest in Irish family history.”

Further information is available at registers.nli.ie.