The most northerly part of the Irish province of Ulster is Malin Head in county Donegal. It is also the most northerly point on the island of Ireland.
The Island of Unst is the most northerly island on Britain.
Ellesmere Island
Northumbria
The most northerly county in Scotland is Caithness.
Hokkaido
If you mean southern Ireland as a reference to the part of island of Ireland that is not Northern Ireland, then yes. The term "southern Ireland" is an incorrect and inaccurate reference to what is more commonly known as the Republic of Ireland. If you mean geographically, then the answer is no, as the most northerly point on the island of Ireland is Malin Head in county Donegal. County Donegal is in the Republic of Ireland, not Northern Ireland. See the map at the link below which shows the counties of the Republic of Ireland in green, and the counties of Northern Ireland in a tan colour. You will see that Donegal is in the Republic of Ireland, not Northern Ireland, and that it has the most northerly point on the island of Ireland.
The most northerly point in Ireland is Malin Head which is in county Donegal.
Martinique
cayman island
Out Stack... or Muckle Flugga
The most northerly county on the mainland of Scotland is Caithness.