The only part of Ireland that is in the UK is Northern Ireland.

Quick Scoop: Which Part of Ireland Is UK?

On the island of Ireland, there are two different political entities.

  • Northern Ireland
    • Located in the north and northeast of the island.
* It is one of the four countries of the United Kingdom (along with England, Scotland, and Wales).
* Its capital city is Belfast, which _is_ in the UK.
  • Republic of Ireland (often just “Ireland”)
    • Covers most of the island (the southern and western parts).
* It is a completely independent country and **not** part of the UK.
* Its capital city is Dublin, which is _not_ in the UK.

So if someone asks “which part of Ireland is UK?”, the precise answer is:

Only Northern Ireland is part of the United Kingdom; the Republic of Ireland is a separate, independent state.

Simple table: Ireland vs UK status

[3][9] [1][9][3] [3] [9][1][3] [1][9][3] [3]
Area On the island of Ireland? In the UK? Capital city
Northern Ireland YesYesBelfast
Republic of Ireland YesNoDublin

“Most of the island of Ireland is an independent state; only Northern Ireland remains within the United Kingdom.”

TL;DR:
If you’re asking “which part of Ireland is UK?” → the answer is Northern Ireland only.

Information gathered from public forums or data available on the internet and portrayed here.