Patrick, one of the world's most beloved Saints, was never formally canonized under the process that we are accustomed to today. When the first list of saints was constructed, Patrick was already recognized by the Church Fathers as a Saint and was automatically placed on the list.
The story of St. Patrick is far more amazing than any of the myths and legends about him. While St. Patrick may not have actually driven the snakes out of Ireland (there never were snakes in Ireland), he did drive out something much more formidable — Druidism. Not only did St. Patrick drive the Druids out of Ireland, he firmly established the Church on Irish soil. The story of St. Patrick is wonderfully retold in the Catholic Encyclopedia.
One legend recounts how St. Patrick taught the Irish about the Trinity by using the shamrock as an example. St. Patrick mused that while there are three distinct leaves on the shamrock, the shamrock is still one.
St. Patrick did not leave a wealth of written records behind. Nonetheless, there are two writing that exist that are recognized my most modern scholars as genuine. These are the "Confessio"and the "Epistola ad Coroticum." The "Confessio," or "The Confession of Patrick," is available on this Web site. Also available is "The Shield of St. Patrick," a writing that has long been attributed to St. Patrick but which cannot be authenticated.