Astronomy Ireland was founded in 1990 and is the largest astronomy society in Ireland. They hold regular talks on a multitude of astronomical topics as well as introductory classes in astronomy. In addition to a monthly magazine for members, they also have a weekly astronomical news program on 102.3 Dublin City FM.
IFAS is the umbrella group for democratically elected amateur astronomy clubs and societies located throughout Ireland. They provide a way for like-minded enthusiasts to share tips, tricks and information through their website, which can be found here. A more complete list of amateur societies who are members of IFAS can be found on this page.
The Irish Astronomical Society was founded in 1937 as a society for amateur astronomers living in or near Dublin. Membership in the society is open to anybody, with membership rates ranging from 20-40 euro per year. Monthly observing sessions are held during the winter months, while classes in astronomy for beginners and telescope construction are also available.