Portmarnock is a coastal town in County Dublin, Ireland, north of the city of Dublin, with significant beaches, a modest commercial core and inland residential estates, and two golf courses, including one of Ireland's best known, Portmarnock Golf Club. as of 2022, the population was 10,750, an increase of 13.5% on the 2016 census figure of 9,466.

Portmarnock is also a civil parish