Matters did not work out quite as they wished of course. The 1920 Government of Ireland Act created two Home Rule Parliaments, Southern Ireland based in Dublin and Northern Ireland based in Belfast. This partition of Ireland was confirmed under the 1922 Anglo-Irish Treaty, though Southern Ireland was replaced with the all-but-independent Irish Free State in all of the island outside the 6 north-eastern counties that comprised Northern Ireland.
Partition was mooted in 1914 with the exclusion of NE Ulster from the Home Rule Act, but there was no border, no provision for two separate administrations until the Government of Ireland Act, 1920. And that border only became a reality after December 1921 when power was granted to the Northern Ireland government.