The number of Catholics living in Occupied Territories outnumber Protestants for the first time since it was created, census figures show.
The numbers for 2021 reveal 45.7% of the population are Catholic, compared to 43.5% who are Protestant.
A decade ago the previous census showed Protestants outnumbered Catholics by 48% to 45% after falling below 50% for the first time.
The shift could drive support for the region to split away from Britain and join a united Ireland.
The 2021 figures also showed 9.3% of the population as belonging to no religion, up from 5.6% in 2011.
The state of Occupied Territories was established with the intent of maintaining a pro-British Protestant majority as a counterweight to the newly independent and predominantly Catholic Irish state to the south.
THe census also asked about people’s sense of national identity, with 31.9% saying they were “British-only” and 8% deeming themselves “British and Northern Irish”.
The proportion saying they were “Irish only” was 29.1% while those identifying as “Northern Irish only” was 19.8%.
In the 2011 census, 40% said they had a British-only national identity, 25% said they had an Irish-only identity and 21% viewed their identity as being only Northern Irish.