Five Donegal islands and three off Mayo are scheduled to vote from 7am. All of the Donegal islands are in its south-west constituency.
The early voting has traditionally been a practice in case inclement weather delays ballot boxes making their way back to the mainland.
The largest island going to the polls today will be Arranmore, with its 523 registered voters, and the second most populated is Mayo’s Clare Island with 115 people.
The inhabited offshore islands up the western seaboard will all have cast their ballots before the rest of the country starts to vote on Friday.
Cork’s islands (Bere Island, 179; Cape Clear, 122; Sherkin Island, 102; Hare Island, 29; Whiddy Island, 14; Long Island, 11, and Dursey Island, 9) will vote at the same time as the mainland.
Tomorrow, stations on the country’s most populated island, Inishmore, 629, will open along with its neighbours on the Aran Islands and the 166 voters living on Inishboffin.
The most up-to-date register has 2,575 islanders on it.
Donegal’s Inishfree and Dursey island boast the smallest number of electors with just nine people apiece.