On 6 December 1922, the Irish Free State left the United Kingdom, with Northern Ireland remaining as part of the United Kingdom of Great Britain and Northern Ireland.
1832–1870 Overall representation for Ireland increased from 100 to 105 with additional seats in Belfast, Galway Borough, Limerick City, Waterford City and Dublin University gained a second seat.
Borough constituencies defined with minor changes by the Parliamentary Boundaries (Ireland) Act 1832.
The general election of 1918 in Ireland was, in British law, to fill the 105 Irish seats in the House of Commons of the United Kingdom for the 31st United Kingdom Parliament.
From the 1922 Westminster election, held on 15 November, only the six counties of Northern Ireland were represented in Parliament.
1922–1950 There was a redistribution of constituencies, following the Anglo-Irish Treaty and the establishment of the Irish Free State.
Twenty-six of the thirty-two Irish counties ceased to be represented in the United Kingdom Parliament.
All seats were single member, except for Antrim, Down and Fermanagh & Tyrone.
The predominant county when the constituency is created is named in those cases.
All seats were single member ones from this time and the university constituency was abolished.
The House of Commons (Redistribution of Seats) Act 1979 increased representation for Northern Ireland from 12 to 17.
1983–1997 The historic counties ceased to be relevant to constituency boundaries.
See List of parliamentary constituencies in Northern Ireland for Antrim, Londonderry, Tyrone, Armagh, Down and Fermanagh.