When did Ireland and Northern Ireland separate?
Partition of Ireland
3 May 1921
The partition of Ireland (Irish: críochdheighilt na hÉireann) divided the island of Ireland into two distinct jurisdictions, Northern Ireland and Southern Ireland. It took place on 3 May 1921 under the Government of Ireland Act 1920. Today the former is still known as Northern Ireland and forms part of the United Kingdom, while the latter is now a sovereign state also named Ireland and sometimes called the Republic of Ireland.