The National Lottery is appealing to lotto players to check their tickets, after €6.2m was won in Drogheda, Co Louth.
The winning ticket of last Saturday night's draw was sold in Tesco Extra on the Donore Road. However, nobody has come forward yet to claim the jackpot.
The winning numbers were 1, 7, 9, 18, 22, 33 and the bonus number was 17.
The National Lottery's Head of Marketing, Michael Hayes, is advising the holder to sign the back of the ticket, put it somewhere safe and contact the prize claims team.
The National Lottery says Louth is now the "luckiest" county for jackpot winners, with the most Lotto millionaires per head of population.
Since it was launched 32 years ago, the county has had 78 Lotto jackpot winners who have won in excess of €97m between them.
And of the four jackpots won so far this year, two have been claimed in Co. Louth.