There are 34.5 million Americans who are primarily or partially Irish—seven times more people than the current population of Ireland. Irish is the second-most common ancestry among Americans, falling just behind German.
That means there is a lot of interest in Irish genealogy. But there are difficulties.
David Ouimette manages the acquisition and online publication of genealogical records worldwide for FamilySearch and frequently lectures a genealogical conferences. He describes the reasons that Irish family history research can be frustrating.
The Roman Catholic faith flourished in Ireland for over fifteen hundred years, notwithstanding opposition. The British government instituted the Penal Laws to weaken the influence and power of the Catholic Church politically and economically. By 1744, the Penal Laws were strictly enforced and made the next few decades especially difficult for Catholics. Priests were forbidden to celebrate mass. Those who did were to be exiled, with the threat of execution if they returned to Ireland.
Priests were instructed to maintain baptismal and matrimonial records as early as 1614. Some early records still survive, but the majority of existing parish registers begin in the 1820s or later. Catholic priests kept records of baptisms and marriages but only rarely kept burial registers.