The originals of almost all Irish sources are in Ireland. However, copies, transcripts and abstracts of many records are available in the UK.
Latter Day Saints Family History centres have access to the microfilm holdings of the main Family History Library in Salt Lake City, Utah in the US. Their most important holdings are Irish General Register Office records and a large, but by no means complete, set of parish records. There are also extensive holdings of census and property records. See
www.familysearch.org.
The Irish Genealogical Research Society Library in London has a varied collection of material, much of it consisting of record transcriptions made by members, some from originals that now no longer exist. Most concern the Anglo-Irish. See
www.igrsoc.org/library-holdings.htm.
CD copies or indexes to many records, including wills, property records and some
civil records are available.