St. Patricks Day is linked to everything Irish: green, gold, shamrocks and luck. So, why is it celebrated on March 17th? One theory is that that is the day that St. Patrick died. Since the holiday originated in Ireland, it is believed that as the Irish spread out around the world, they took with them their history and celebrations. In American cities with a large Irish population, St. Patrick's Day is a big deal. People in the US celebrate with parades, music and songs, Irish food and drink, and activities for kids such as crafts, coloring and games. Most people wear green or they will be pinched that day.