As An_chilleasrach says, FitzGerald's study is worth a look.
quote:I would guess that the Galway side would have made the switch to Béarla more recently, but from what my relatives tell me, it was still before 1900.
Clifden and the surrounding area was in the Barony of Ballynahinch. According to the 1851 census, 85.4% of residents in the Barony were Irish speakers. Almost 40% of the Irish speakers were monoglots (Irish-only). In the census of 1891, 74% of the population were recorded as Irish speaking, though the number of monoglots had been reduced significantly.
I doubt you'll be able to pinpoint it exactly, but you'd want to find out the occupation of the head of the household, their religious background etc, if you don't already know. That could help.
As for Longford, the Barony with the highest percentage of Irish speakers in 1851 was Granard at 3%.