Among them were customers at the Salt House Bar in Galway, who were celebrating when something out of the ordinary happened.
"I was cleaning up glasses and felt a drip on my head and we noticed that it was raining from the roof," said Liam McEvoy, who was working in the bar.
He went upstairs to the storeroom and discovered a keg had burst.
"When 20 litres of beer comes out of the keg there's a lot of it, so it spread across the floor upstairs and started to come through in a few different spots," he said.
Liam said staff cleared up the spill pretty quickly, but that did not stop some of the beer from raining down on customers in the bar.
"It was unfortunately just over two tables of girls, so we just gave them umbrellas and let them get on with their day," he said.
"At first everyone was a bit unsure what was happening, but it was St Patrick's Day so nobody was really going to complain or go home and they got a bit of a laugh out of it, getting served with umbrellas up in the pub even if it's bad luck.
"I think beer from the roof was strange enough, let alone having superstitions."
Eventually the drips subsided, but the female drinkers had got quite used to the novelty of using umbrellas indoors.
"I think the girls started to enjoy it so they kept them up for about half an hour, even though they probably only needed them for a few minutes," he said.
Irish people around the world raised a glass or two in honour of their patron saint on St Patrick's Day.