In Ireland, St. Patrick's Day is a religious holiday, similar to Christmas and Easter.
There are 33.7 million U.S. residents who are of Irish ancestry. That's almost nine-times the population of Ireland, itself.
Nineteen U.S. Presidents proudly claim Irish heritage including our first president, George Washington.
The very first St. Patrick's Day parade was not in Ireland, but in Boston in 1773. The largest parade in the United States held since 1762 is in New York City. In 1948, President Harry Truman became the first president to attend a St. Patrick's Day parade.
The city of Chicago goes all out celebrate, dyeing their river green.
The color green is associated with St. Patty's Day because it is the color of spring in Ireland and the shamrock, of course.
That's America by Numbers -- St. Patrick's Day.