The parliament of Northern Ireland exercises its option to opt out of the Irish Free State and petitions King George V:

“MOST GRACIOUS SOVEREIGN, We, your Majesty’s most dutiful and loyal subjects, the Senators and Commons of Northern Ireland in Parliament assembled, having learnt of the passing of the Irish Free State Constitution Act, 1922, being the Act of Parliament for the ratification of the Articles of Agreement for a Treaty between Great Britain and Ireland, do, by this humble Address, pray your Majesty that the powers of the Parliament and Government of the Irish Free State shall no longer extend to Northern Ireland.”

Thus six counties of the north of Ireland – Antrim, Armagh, Tyrone, Down, Fermanagh, Derry become an autonomous entity of Northern Ireland within the United Kingdom.

When Michael Collins and colleagues agreed to the treaty in December 1921, they believed that a promised Boundary Commission would significantly alter the partition of Ireland and drastically reduce the size of the proposed Northern Ireland. The Boundary Commission proved to be totally ineffective and Northern Ireland remained as six counties. The first Prime Minister of Northern Ireland was hard-line unionist James Craig who was to state “All I boast of, is that we are a Protestant Parliament and a Protestant State,” echoing to some extent what De Valera would state later about the Catholic Irish Free State.