The Vikings invaded Ireland in the 9th Century and historical records tell us that they occupied Carlingford Lough. The very name Carlingford is Scandinavian translating into ‘Fjord of Carlinn’. They may have used the sheltered natural harbour of Carlingford as a temporary base though this is speculation as no factual evidence, apart from the name, has been recovered so far.The Normans arrived in Ireland in 1169 as allies of an Irish King Dermot MacMurrough. By 1184 they had made their way to Carlingford. A Norman Knight, John de Courcy claimed this part of Louth for himself.
The very first historical reference to Carlingford that we know of dates to 1184 when he gave the rights of the ferry at Carlingford to the Abbot of Downpatrick which indicates that the harbour or somewhere near it was in use as a ferry point. However, the town of Carlingford only developed after the castle known as King John’s Castle was built, reputedly by Hugh de Lacy son-in-law of Bertram de Verdun who had been assigned the territories taken from John de Courcy by Henry II.