Firefighters, police officers, high school and military bands, step dancers, men in kilts and many Irish-for-the-day snaked along the parade route from 44th to 86th Street to the wail of bagpipes on a sunny, but chilly day.
"It's fantastic," said Damian McKevitt, another Northern Ireland resident who came to New York just for the parade. "It's Fifth Avenue, that's just huge."
The parade typically draws 2 million spectators and 150,000 marchers, and even though New York boasts the nation's largest parade, other cities also pulled out the stops.
In Indianapolis, Mayor Greg Ballard poured green dye into the newly cleaned downtown canal prior to that city's parade.
In Ohio, some 10,000 marchers were enlisted for a Cleveland parade that dates back to 1867.
In Columbus, the Roman Catholic bishop asked the Shamrock Club not to hold its parade on St. Patrick's Day out of deference to Holy Monday; the group refused but did change the march route.
Some parades were held Saturday; Sinn Fein President Gerry Adams marched in Buffalo.
In Ireland, half a million Dubliners and visitors gathered five deep to enjoy their parade, the centerpiece of a five-day festival.
But not everyone was celebrating in New York. Some gay and lesbian protesters held up signs along the parade route, angered by the parade committee's continued refusal to allow gay and lesbian groups to march under their own banners.
And the usual large contingent of politicians was absent this year, with Mayor Michael Bloomberg and other officials in Albany for the swearing-in of Gov. David Paterson, who became New York's 55th chief executive Monday after Eliot Spitzer resigned in disgrace last week after being implicated in a prostitution investigation.
Just blocks from the parade, a neighborhood near the U.N. that was virtually shut down over the weekend because of a deadly crane accident on Saturday struggled to get back to normal.
There are at least half a dozen Irish bars on Second Avenue near the accident scene, and the ones that were open were packed with revelers. Michael Mullooly, manager of Jameson's Pub, noted that the death toll could have been much higher if the crane collapsed Monday. "If it happened today there would be carnage," he said.
But back on Fifth Avenue, Irish eyes were smiling.
Dublin resident Alan Murray had persuaded his two sisters to come with him to the U.S. to see the parade.
"We have to go to New York for Paddy's Day because it's brilliant," said Murray, whose face was painted orange, white and green, the colors of the Irish flag.
His sister Carol, wearing a feather boa in the same colors, agreed. "Everyone makes more of an effort here," she said.