| Hillsborough Castle|
9 December 1922
| Lord Lieutenant of Ireland|
The 3rd Duke of Abercorn
The Governor of Northern Ireland was the principal officer and representative in Northern Ireland of the British monarch. The office was established on 9 December 1922 and abolished on 18 July 1973.
Governor of Northern Ireland Wikipedia
The office of the Governor of Northern Ireland was established on 9 December 1922 under Letters Patent to:
do and execute in due manner as respects Northern Ireland all things which by virtue of the  Act and our said Letters Patent of 27 April 1921 or otherwise belonged to the office of Lord Lieutenant at the time of the passing of the Irish Free State Constitution Act 1922.
The Governor had possession of the Great Seal of Northern Ireland.
The Governor was the successor to the Lord Lieutenant of Ireland in Northern Ireland, itself established on 3 May 1921. The office of the Governor was abolished on 18 July 1973 under Section 32 of the Northern Ireland Constitution Act 1973. The Secretary of State for Northern Ireland, a cabinet office that had been created in 1972, took over the functions of the Governor on 20 December 1973 under Letters Patent.
The official residence of the Governor of Northern Ireland was Hillsborough Castle in County Down. Following refurbishment of the Castle, the Duke of Abercorn took up residence in 1925. It remained the official residence until the abolition of the office of Governor in 1973; henceforth it has been the official residence of the Secretary of State for Northern Ireland.