The theme of this year’s event, the largest in the country, was “extraordinary world”, and young and old alike seemed delighted with the colour and noise as the parade snaked its way through the city centre.
Hundreds of thousands of people gathered in towns and villages for more than 180 special events marking the occasion.
Beginning in Parnell Square just after noon, the Dublin parade was led by Grand Marshal Packie Bonner, the Irish goalkeeping legend.
More than 3,000 performers took part in the parade, which made its way along the 3km route under warm spring sunshine.
Shamrock-painted faces and novelty hats filled the capital’s streets, with some brave bystanders dangling from lampposts to catch a better view of the festivities.
Stall owner Noel Owens was among those enjoying a roaring trade in memorabilia at his stand outside Trinity College.
“I’m always proud to be Irish but especially on Patrick’s Day – people come from all over the world to be here for this parade.”
On Dame Street Tim Parks from Dundalk, Co Louth, brought his two young children along to enjoy the spectacle.
“We’ve met people from China and India and they’re all dressed in green so there’s a great sense of fun,” he said.
“I think in the current economic climate it’s a chance for people to forget the recession for the day and maybe drown their sorrows in a green Guinness.”
In Belfast, musicians, performers and community groups danced through the city as St Patrick’s Day was marked in style.
In Limerick, the parade was led by Grand Marshal rugby star Keith Earls. Riding in the back of a Rolls Royce, the Irish back tossed 250 signed small rugby balls into the crowd, which was estimated at more than 70,000.
“They gave me 250 balls to sign two weeks ago so I had plenty of time,” he said.
Cuddling his little sister Jenny, 3, Keith said: “It’s massive – just like the great roar at a big rugby game.”
Keith’s throw-in to the crowd was accurate when he spotted a group of school friends from Moyross.
Cian Kirby, a 7-year-old member of Garryowen club, caught the first ball shouting: “I’ve got it.”
Two horses not of the Cheltenham variety earned huge applause.
Standing 12 feet high they were made by 46 children who attend five primary schools on the northside of the city. Each day after school they attend the Northside Learning Hub.
Hub organiser Gina Brocker said: “We started work on the horses after Christmas and made them from recycled insulation materials, wire and bamboos. We get help from mentors who come from third-level colleges in the city.”