St. Patrick, the primary patron saint of Ireland, is synonymous with the Emerald Isle, having converted the largely pagan society to Christianity in the fifth century. In the centuries that have followed, legends have sprung up surrounding his life, including that he drove all the snakes out of Ireland, used the shamrock to teach the Irish about the Holy Trinity, and was captured by Irish pirates and enslaved at the age of 16.
While there is no historical evidence that he drove snakes out Ireland or ever referenced shamrocks, according to St. Patick's autobiography, he was indeed kidnapped from his birthplace in Roman Britain and forced to work as a sheep herder in Ireland for six years.
The autobiography, titled "Confessio," provides details surrounding his family, birthplace, and journey back to Ireland after escaping slavery. It began [translation via Christian Classics Ethereal Library]:
I, Patrick, a sinner, a most simple countryman, the least of all the faithful and most contemptible to many, had for father the deacon Calpurnius, son of the late Potitus, a priest, of the settlement [vicus] of Bannavem Taburniae; he had a small villa nearby where I was taken captive. I was at that time about sixteen years of age. I did not, indeed, know the true God; and I was taken into captivity in Ireland with many thousands of people, according to our deserts, for quite drawn away from God, we did not keep his precepts, nor were we obedient to our priests who used to remind us of our salvation. And the Lord brought down on us the fury of his being and scattered us among many nations, even to the ends of the earth, where I, in my smallness, am now to be found among foreigners.
The modern-day location of the "settlement of Bannavem Taburniae" has long been contested; experts have not reached any definitive conclusion, as of this writing. As explained in "Saint Patrick Retold" by Roy Flechner:
As for his place of birth, we are told in Confessio that the family hailed from the town Bannavem Taburniae and that his father also owned a small villa (villula). The exact whereabouts of the town and villa are unknown, although they occasioned much speculation in both medieval and modern times, ranging from Thomas O'Rahilly's identification of Bannavem Taburniae with Glastonbury to Charles Thomas's suggestion that it may have been Birdoswald (Banna), towards the western end of Hadrian's Wall, approximately 20 kilometres east of Carlisle.
After six years as a slave in Ireland, he managed to flee back to his homeland and reunite with his family. In one of the most famous passages of "Confessio," he tells of a dream he had that inspired him to return to Ireland and become a missionary.
I saw a man coming, as it were from Ireland. His name was Victoricus, and he carried many letters, and he gave me one of them. I read the heading: "The Voice of the Irish". As I began the letter, I imagined in that moment that I heard the voice of those very people who were near the wood of Foclut, which is beside the western sea—and they cried out, as with one voice: "We appeal to you, holy servant boy, to come and walk among us.
In sum, while it is uncertain as to which town in Roman Britain St. Patrick was born in, historians know from his autobiography, "Confessio," that he was not Irish, nor was he born in Ireland.