Its major beach, the Velvet Strand, is monitored by a lifeguard during the summer season from early April to the start of October.

On 23 June 1930, Australian aviator Charles Kingsford Smith and his crew took off in the Southern Cross on the second westbound transatlantic flight (to Newfoundland), after which they continued on to Oakland, California, completing a circumnavigation of the world.

The first solo westbound transatlantic flight began from Portmarnock beach when Jim Mollison, a British pilot, took off in a de Havilland Puss Moth on 18 August 1932 bound for Pennfield Ridge, New Brunswick, Canada.

[6] The sculpture Eccentric Orbit (by Rachel Joynt and Remco de Fouw, erected 2002) on the seafront is of limestone, bronze and stainless steel.

The area had been settled in Neolithic times, as evidenced by flints and other tools excavated on the northern fringe of Portmarnock and the remains of a ring fort visible from the air at the south of the town.

[10] In February 1988 An Garda Siochana discovered a Provisional IRA arms cache at Station Road.

[22] St. Marnock's was largely built in the late 1890s to the designs of British architect Sir Robert Lorimer.

[citation needed] Portmarnock Pitch & Putt Club was founded in 1958 and moved to its current location in 1961.