Republic of Ireland–United Kingdom border
Originally intended as an internal boundary within the United Kingdom of Great Britain and Ireland, the border was created in 1921 under the United Kingdom Parliament's Government of Ireland Act 1920. Prior to this, a separatist Irish parliament had been established in Dublin, which did not recognise the Government of Ireland Act, and was actively engaged in the Irish War of Independence. The Act was intended to deliver Home Rule in Ireland, with separate parliaments for Southern Ireland (which included three of the nine counties of Ulster) and Northern Ireland. Six of the thirty-two counties of Ireland were assigned to Northern Ireland, and the rest of Ireland comprising 26 counties to Southern Ireland.
Administrative counties of Ireland
Administrative counties were a unit of local government created by an Act of the Parliament of the United Kingdom for use in Ireland in 1899. Following the separation of the Irish Free State from the United Kingdom of Great Britain and Ireland, administrative counties continued in use in the two parts of the island of Ireland under their respective sovereign jurisdictions. They continued in use until 1973 in Northern Ireland and until 2002 in the Republic of Ireland.