The name Carrickfergus derives from the Gaelic  'Carraig Fear gusa' which translates to  'Rock of Fergus',  named after King Fergus of Dalriada (498AD). The kingdom he ruled stretched along the North Antrim coast and into Argyll and Bute in Scotland. Fergus had moved the seat of power from Ireland to Scotland, on one journey back to Ulster in stormy weather his boat foundered on the long rock 'carrick' where he was drowned. References are made to Fergus having leperosy and that he was returning to seek a cure.

The same long rock which in geological terms is a volcanic dyke, served as the foundations for Carrickfergus Castle built by John de Courcy in the 1180s. This magnificantly preserved castle strategically guards the entrance to Belfast Lough and has served as the stronglhold for numerous governers and conquerers, and indeed has also been beseiged at different times during its history by French, Scots, English and Irish troops. The castle would have originally been surrounded by water. De Courcy also founded St Nicholas Church in 1192 and Woodburn Priory.

The castle and Carrickfergus remained in the ownership of De Courcy until 1203 when he was overthrown by Hugh De Lacy with the blessing of King John. Hugh De Lacy became the First Earl of Ulster in 1205 and added the gatehouse, towers and outer walls to the castle, he also endowed the Franciscan Friary. He eventually lost the castle in 1210 when King John arrived in Carrickfergus and forced him to flee to Scotland, this was after a war broke out between the Earl and FitzHenry, the King's Judiciar in Ireland. The castle was returned to De Lacy in 1227 where he lived until his death in 1242.

The history of Carrickfergus Castle makes fascinating reading and spans some 800 years, its walls has seen many Kings and Earls come and go. In May 1315, Edward the Bruce arrived at Olderfleet (Islandmagee) just acorss the water from Larne harbour. He arrived with a well seasoned army to take up an invitation  by the Irish Earls to become King of Ireland and help remove English rule. The Earls had been inspired by the victory at Bannockburn of Robert and Edward Bruce which led to Robert being crown King of Scotland.