On which website(s) are official announcements published?
Irish Government Publications website
Irish government publications from government departments and agencies, including news, press releases, and reports.
https://www.gov.ie/en/publications/
Iris Oifigiúil
Iris Oifigiúil is the official means used by the Irish Government for announcing appointments to public offices and publishing proclamations, statutory instruments, appointment of receivers to companies, etc.
Prima Facie evidence of any proclamation, order, rule, regulation, bye-law, or other official document may be given in any legal proceedings by production of a copy of the Iris purported to contain such matter (Documentary Evidence Act 1925 ss.3-4). Notices in relation to many matters concerning companies must be published in the Iris within six weeks of the delivery to the Registrar of Companies. (S I No 163 of 1973; Companies Amendment Act 1983 s.55).