The earliest formulations of Irish law are thought to originate from seventh/eighth century Irish society - but the earliest surviving manuscript copies of them date from several centuries later.
Multi-volume collections in the Law Bod include
Corpus Iuris Hibernici
Ancient laws of Ireland aka Brehon laws (editions of manuscripts written by Christians recording the earlier Irish tradition)
Lost and Found in Early Irish Law by Primary Sources
Multi-volume collections of "legislation" in the Law Bod include
Corpus Iuris Hibernici
Ancient laws of Ireland aka Brehon laws (editions of Mss written by Christians recording the earlier Irish tradition)
Statute Rolls of Ireland (temp King John to Henry VIII)
The Irish Statutes - legislation of the pre-Union Irish parliament 1310 (3 Edw II) to the Union (1800)
Statutes of the United Kingdom of Great Britain and Ireland 1801 to 1922
Free state & Republic legislation to date
Indexes to Irish legislation at Ireland 30
Statutes of the Irish Parliament from Richard III - Henry VII by Commentary
Law Bod's working collection of Irish law is on Floor 2
KL403 is where works just on the history of Irish law (all periods) can be found. Depending on what aspect of Irish legal history you are studying, don't just limit yourself to this collection. Remember the subject classification scheme for monographs. Works, for example, on Irish land law will be shelved under the topic KN62 with the geographic indicator I5 in the shelf mark.
Law journals which may have articles of interest:
IJ or I Jur - Irish Jurist OS vv.1-31 (1935-1965) Ireland 300 I50 (sec coll)
IJ or I Jur - Irish Jurist NS v.1 onwards Ireland 300 I50
NILQ Northern Ireland Legal Quarterly Cw UK NI 300 N20 ( HeinOnline has full text for all but the two most recent volumes which are indexed only)
eg Hand, G. J. “English Law in Ireland, 1172–1351.” Northern Ireland Legal Quarterly 23 (1972): 393.
The Laws and Other Legalities of Ireland, 1689-1850 by 
Guardian of the Treaty : the Privy Council Appeal and Irish sovereignty by