The National Lottery has confirmed that the winning ticket in the Lotto Plus 1 draw on Saturday was sold in Castlebar.
The ticket is worth €1 million euro.
A national lottery spokesperson has confirmed to Midwest News that it was a quick pick ticket bought on Friday.
The shop that sold the winning ticket will be named tomorrow.
No one has yet come forward to claim the prize.
The main Lotto weekend jackpot was €6.4 million, and the winning ticket in that draw was sold in Athlone.
It was a quick pick ticket bought on Thursday.
Lotto players in the Castlebar and Athlone areas are being urged to check their tickets carefully.
The winners should sign the back of the tickets and keep them in a safe place while contacting the National Lottery prize claims team.