The EuroMillions Plus top prize of 500,000 euro was won in Cork last night.
Dunnes Stores in the Bishopstown Shopping Centre sold the winning ticket on Thursday.
The National Lottery are urging players to check their tickets carefully.
Last night's winning EuroMillions Plus numbers were: 01, 14, 19, 21 and 38.
The winning ticket holder is advised to sign the back of their ticket and keep it in a safe place as it is now worth half a million euro.