One traditional icon of the day is the shamrock. And this stems from a more bona fide Irish tale that tells how Patrick used the three-leafed shamrock to explain the Trinity. He used it in his sermons to represent how the Father, the Son, and the Holy Spirit could all exist as separate elements of the same entity. His followers adopted the custom of wearing a shamrock on his feast day.
The St. Patrick's Day custom came to America in 1737. That was the first year St. Patrick's Day was publicly celebrated in this country, in Boston.
Today, people celebrate the day with parades, wearing of the green, and drinking beer. One reason St. Patrick's Day might have become so popular is that it takes place just a few days before the first day of spring. One might say it has become the first green of spring.