It's mainly only the West of Ireland - Galway, Mayo, Donegal, Kerry mainly and some in Cork and a little pocket in Meath where Connemara natives ended up....

From Wiki: "The Meath Gaeltacht has a history quite different from that of the country's other Irish speaking regions. The Ráth Cairn Gaeltacht was founded in 1935 when 41 families from Connemara in West Galway were resettled on land previously acquired by the Irish Land Commission. Each was given 9 hectares (22 acres) to farm. Baile Ghib (formerly Gibbstown) was settled in the same way in 1937, along with Baile Ailin (formerly Allenstown). In the early years, a large percentage of the population returned to Galway or emigrated, but enough Irish speakers remained to ensure that Ráth Cairn and Baile Ghib were awarded Gaeltacht status in 1967. The original aim of spreading the Irish language into the local community met with no success, and the colonists had to become bilingual.[38]"

But ya no Gaeltacht in Northern Ireland, but lots of Catholics would learn and love the language.