I'm not sure where the divides are.
Like Breandán said they go into each other like a spectrum.
There's Cois Fharraige, which probably goes as far as Ros a'mhíl (again not sure).
Then from Ros a'mhíl to An Cheathrú Rua to where you turn off to the Islands is another mini-dialect.
Then there's the Islands (Ceantar na nOileáin, Ros Muc).
Carna Cill Chiaráin areas are call Iorras Aithneach.
All of them are really mini-dialects with little between them.
Some words are pronounced slightly differently. Some dialects might have words that the others don't have. You'd need a good ear (like our Benjamin) to tell the difference between them.
The differences would more likely perceived between Iorras Aithneach and Cois Fharraige. Again I'm not an expert.
For example-
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..
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