1820 in Ireland

Events

• 30 January – Irish-born Royal Navy captain Edward Bransfield in the Williams is the first person positively to identify Antarctica as a land mass.
• 12 February – the East Indian and Fanny set sail from Cork with settlers for the Cape Colony.
• 6 May – failure of Newport's Bank in Waterford.
• 25 May – failure of Roche's Bank and stoppage of Leslie's Bank in Cork.
• 3 June – the Roman Catholic Cathedral of St Mary and St Anne in Cork is largely destroyed by arson.
• 8 July – act for lighting the city and suburbs of Dublin with gas.
• 20 July – Saint Cronan's Boys' National School opens in Bray, County Wicklow, as the Bray Male School.
• December – Lough Allen Canal, giving through navigation between Carrick-on-Shannon and Lough Allen, opens.
• The Royal Dublin Society adopts its "Royal" prefix when the new king George IV of the United Kingdom becomes its patron.
• Suspension of construction of the Wellington Testimonial, Dublin, in Phoenix Park to the design of Robert Smirke.
• First steamship on the Irish Sea crossing from Dublin to Liverpool, the Waterloo, introduced by George Langtry of Belfast.
• Frederick Bourne begins to create the village of Ashbourne, County Meath.
• Publication of James Hardiman's The History of the Town and County of the Town of Galway, from the earliest period to the present time in Dublin.

  Arts and literature

• Charles Maturin publishes Melmoth the Wanderer.
• Regina Maria Roche publishes The Munster Cottage Boy: a Tale.

  Births

• 19 February – John Tuigg, third Roman Catholic Bishop of Pittsburgh, Pennsylvania.
• 31 May – Timothy Burns, Lieutenant Governor of Wisconsin from 1851 to 1853.
• 3 June – Thomas William Moffett, scholar, educationalist and President of Queen's College Galway.
• 4 June – John Kean, businessman and politician in Ontario.
• 2 August – John Tyndall, physicist.
• 6 October – James Travers, soldier, recipient of the Victoria Cross for gallantry in 1857 at Indore, India.
• 22 November – Katherine Plunket, botanical artist and longest-lived Irish person ever.
• 30 December – Mary Anne Sadlier, novelist.
• ;Full date unknown
• :*Thomas Bellew, Galway landowner and politician.
• :*Johnston Drummond, early settler of Western Australia, botanical and zoological collector.
• :*Ambrose Madden, recipient of the Victoria Cross for gallantry in 1854 in the Crimea, at Little Inkerman.
• :*Patrick Mylott, soldier, recipient of the Victoria Cross for gallantry in 1857 in India.
• :*Henry Hamilton O'Hara "Mad O'hara", "The Mad Squire of Craigbilly".
• :*Kivas Tully, architect.

  Deaths

• 29 January – George III of the United Kingdom of Great Britain and Ireland.
• 5 February – William Drennan, physician, poet, educationalist and co-founder of the Society of United Irishmen.
• 13 February – Leonard McNally, informant against members of the Society of United Irishmen.
• 20 March – Eaton Stannard Barrett, poet and author.
• 6 June – Henry Grattan, member of Irish House of Commons and campaigner for legislative freedom for the Irish Parliament.
• Undated – Anthony Daly, a leader of the Whiteboy movement, hanged for attempted murder.