1804 in Ireland

Events

• 14 January – Richard Lovell Edgeworth's semaphore line between Dublin and Galway is operational, but is out of use by the end of the year.
• 11 February – the last armed rebel group of the Society of United Irishmen, led by James Corcoran, is betrayed and killed or captured by yeomen near Enniscorthy.
• 4-5 March – Castle Hill convict rebellion in New South Wales led by Irish convicts in Australia.
• April – first boat passes through the Grand Canal throughout between the River Liffey in Dublin and the River Shannon.
• 14 May – Cork Street Fever Hospital, Dublin, opens in Cork Street, Dublin.
• First Martello Tower erected in Ireland, at Sutton, Dublin.

Births

• Early February – James Bronterre O'Brien, Chartist leader, reformer and journalist.
• 4 April – Andrew Nicholl, painter.
• 7 April – James Emerson Tennent, politician and traveller.
• 18 November – John George, politician, judge and in 1859 Solicitor-General for Ireland.
• 25 December – Frederic Trench, 2nd Baron Ashtown, peer.
• 26 December – Sir Joseph Napier, 1st Baronet, Conservative Party MP and Lord Chancellor of Ireland.
• 31 December – Francis Sylvester Mahony, humorist and poet .

Deaths

• February – James Corcoran, rebel leader.
• 27 July – Robert Clements, 1st Earl of Leitrim, politician.