Apparently the Irish, especially the Irish-Americans. They've been having parades in America since before the Declaration of Independence was signed! The very first St. Patrick's Day Parade occurred, as best as I can tell, in Boston in 1737. New York's first, in 1762 (or 1766 according to Wikipedia), was similar, a far cry from what it is now. Just some Irish soldiers serving in the British military going on parade for the patron saint's feast day.
Even General George Washington saw a need to recognize St. Patrick's Day for his Irish soldiers. On March 17, 1780 he declared a holiday as “an act of solidarity with the Irish in their fight for independence.”
Read more: http://www.foxnews.com/story/2009/03/17/st-patrick-day-facts-and-legends/#ixzz2Ni6SC4at
But the idea caught on, and not just in New York. Philadelphia's parade started in 1771 and by the 1800s parades had sprung up in most major cities.
And so does Dublin, Ireland. You can even watch a live feed of the parade (on Sunday, March 17) if you can't make it there.
Happy St. Patrick's Day!