Ireland was evangelized in the 400s by missionaries from Roman Britain. The first bishop of Ireland was actually St. Palladius. St. Patrick was the second bishop of Ireland. Other famous Irish saints include
St. Brendan the Navigator (believed to have visited America)
St. Brigid of Kildare (created famous St. Brigid's cross)
St. Columkille (Columba) of Iona, Apostle to the Picts