Killyleagh (Cill O Laoch) is a former fishing village dominated by the impressive castle (closed to the public) of the Hamilton family. Built originally by John de Courcy in the 12th century, the Scottish-baronial-style reconstruction of 1850 sits on the original Norman motte and bailey. Outside the gatehouse, a plaque commemorates Sir Hans Sloane, the naturalist, born in Killyleagh in 1660, whose collection was the basis for the founding of the British Museum (London's Sloane Square is named after him). The parish church houses the tombs of members of the Blackwood family (marquesses of Dufferin), who married into the Hamiltons in the 18th century.
In September the Magnus Barelegs Viking Festival features processions, craft fairs, live music and a Viking boat race on nearby Strangford Lough.