Up to 400,000 people are expected to attend the parade in Dublin, returning after it was cancelled for two successive years due to the pandemic.
In Belfast, the first parade since 2019 will leave City Hall at 1pm. Organisers say the theme will be “We are all Patrick, we are all Belfast”.
What about a parade in Leeds?
In Leeds, the St Patrick's Parade began at Millennium Square on Sunday, March 13.
It was the first large-scale event held to celebrate St Patrick's Day in two years.
Eight floats from local primary schools and organisations were transported across the city centre for the parade this morning, followed from Millennium Square all the way to Vicar Lane by three pipe bands and a walking band.
Over at their starting point hundreds of spectators sang and danced along to traditional Irish jigs, performers as young as three years old taking to the stage on behalf of the Academy of Irish Dance.
Treasurer of the Leeds St Patrick's Day Parade Committee Mark Sexton said:
"It's absolutely fantastic, this has been one of the biggest crowds we have ever had at the parade.
"Leading up to it we knew there was a lot of support and enthusiasm [after Covid] so we created a bigger event than we normally would have.
"Irish people love to celebrate Saint Patrick's Day all over the world and here in Leeds there is a really proud Irish community and lots of other communities that join up [at the parade]."
Are there any celebrations being held in Leeds today?
Yes! The Leeds Irish Centre is hosting a St Patrick's Day party at its home in York Road (LS9 9NT).
There will be live music from The Tradition as well as Cronin, Leeds 15 - 18 Ceile Band, Declan McNulty and other guests.
Elsewhere in the city, there are St Patrick's Day themed nights at clubs like Manahatta and Popworld, South Milford pub Queen o' t' owd Thatch have a 6-course Irish tasting menu, and Call Lane favourite Oporto are hosting a St Patrick's Day weekend with live music, DJs all weekend, Irish decor and hats and plenty of "Guinness goodies and Slane Whiskey".
Howlin’ Ric & the Rocketeers will also be playing on Thursday night promising a "wild night of (sham)rock & roll".
Who is St Patrick and why do the Irish celebrate St Patrick's Day?
Saint Patrick is the patron saint of Ireland.
Saint Patrick was born in the 5th century in Roman Britain and was kidnapped at the age of 16 and sent to Ireland as a slave.
It is said that he managed to escape and then became a missionary.
Saint Patrick is credited with bringing Christianity to parts of Ireland.
One of the emblems of Irish culture, the shamrock is a native type of clover that has three leaves.
It is said that Saint Patrick used the plant to explain the concept of the Holy Trinity - the Father, Son and Holy Spirit
It is believed he died on March 17, 461, which is why it is celebrated on this date.
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