Polling stations have opened around the county for people to cast their vote in the referendum on whether to replace or retain the Eighth Amendment which provides for the equal right to life of the mother and the unborn.
The polls will be open from 7am and will close at 10pm tonight.
See also: Advice when going to vote
Ballots will be cast at more than 6,500 stations across the country.
Voters are being advised to bring their polling card along with identification such as a driver's license or passport. Those without a polling card should bring identification and also proof of address.
In one polling station in Letterkenny, 4% had voted by 9am.
Some people across the county opted to vote on their way to work this morning.
Voting took place on Donegal's islands yesterday