As explained by Roz McCutcneon in her BIFHSGO conference talk, and her handout, the Registry of Deeds is a vast archive, which covers the whole island of Ireland. As of the date of her talk, there were 436,699 names indexed at www.irishdeedsindex.net drawn from 45,975 deeds. The latest update is 452,604 index records from 47,489 deeds. That’s as of 7 November.
These and the subsidiary indexes are fully searchable for free at https://irishdeedsindex.net/search/search.php/.
They provide an entree to the 2686 free-to-view films from the beginning of the Registry in 1708, up to 1929 at: https://www.familysearch.org/search/catalog/185720?availability=Family%20History%20Library.