Events from the year 1620 in Ireland.

• Monarch: James I

• County Longford is planted by English and Scottish landowners, with much of the O'Farrell lands being confiscated and granted to new owners.
• Bangor, County Down, is granted the status of a port by King James I of England.

• 13 October – the Blundell Baronetcy is created in the Baronetage of Ireland in favour of Francis Blundell, Vice-Treasurer and Receiver-General of Ireland.^[1]
• 10 November – the Parsons Baronetcy, of Bellamont in the County of Dublin, is created in the Baronetage of Ireland in favour of William Parsons, Surveyor General of Ireland.
• 12 December – the title of Earl of Antrim is created in the Peerage of Ireland in favour of Randal MacDonnell, Viscount Dunluce.
• The titles of Earl of Cork and Viscount of Dungarvan are created in the Peerage of Ireland in favour of Richard Boyle, Lord Boyle.
• The title of Viscount Grandison is created in the Peerage of Ireland in favour of Oliver St John, Lord Deputy of Ireland.

• Peter Talbot, Archbishop of Dublin (Roman Catholic) (d. 1680)
• Approximate date – Redmond O'Hanlon, outlaw (d. 1681)

• February 15 – James Archer, Jesuit (b. 1550)
• July 10 – John Boyle, Bishop of Cork, Cloyne and Ross (b. 1563?)