Last night's €12.7 million Lotto winning ticket was sold in a shop in Kilkenny.
The winner purchased a Quick Pick ticket and players are now being urged to check their numbers.
The National Lottery says it plans to reveal the shop that sold the ticket over the coming days.
Yesterday's jackpot was the largest in nearly four years.
The winning numbers were 4, 14, 20, 23, 27, 37 and bonus 39.