The town had been officially renamed Kingstown in 1821 in honour of a visit by the British King George IV, but reverted to its ancient Irish name by resolution of the town council in 1921, one year before Irish independence. The name derives from its founder, Laoghaire, a 5th-century High King of Ireland, who chose the site as a sea base from which to carry out raids on Britain and France. Dún is an Irish word meaning "fort". King Laoghaire is famous for having allowed Saint Patrick to travel the country and preach Christianity.
The harbour is notable for its two granite piers. The East Pier is particularly popular with walkers. Other features of the town include a Martello tower known as the James Joyce Tower and the National Maritime Museum of Ireland.
Dún Laoghaire harbour is home to four yacht clubs. From north (West Pier) to south (East Pier) they are the Dún Laoghaire Motor Yacht Club, the National Yacht Club, the Royal Irish Yacht Club, and the Royal St. George Yacht Club.