Monday, March 17 is St. Patrick's Day, celebrating all things Irish in the U.S. and around the world. But it wasn't always a day for partying.

It was a sea of green and gold in St. Paul on Monday as thousands gathered to celebrate the city's annual St. Patrick's Day parade. "It's beautiful to see everyone wearing green — no matter what your nationality or where you're from," Dan Kelly said.

St. Patrick’s Day, the annual celebration of all things Irish, is being marked in cities across the country on Monday with boisterous parades and celebrations. New York City hosts one of the largest and oldest parades in the United States.