As an urban settlement, Carrickfergus far pre-dates the capital city Belfast.
The historical walled town originally occupied an area of around 97,000 square metres, which now comprises the town centre, bordered by Albert Road to the west, the Marine Highway to the south, Shaftesbury Park to the north and Joymount Presbyterian Church grounds to the east. Segments of the town wall are still visible in various parts of the town and in various states of preservation. Archaeological excavations close to the walls' foundations have yielded many artefacts that have helped historians piece together a picture of the lives of the 12th and 13th century inhabitants.
Carrickfergus became an inhabited town shortly after 1170, when Anglo Norman knight John deCourcy invaded Ulster, established his headquarters in the area and built Carrickfergus Castle on the rock of Fergus in 1177. The castle, which is the most prominent landmark of Carrickfergus, is widely known as one of the best-preserved Norman castles in Ireland.
Sometime between 1203 and 1205, De Courcy was expelled from Ulster by Hugh de Lacy, as authorised by King John. De Lacy oversaw the final construction of the castle, which included the gatehouse, drum towers and outer ward. It was at this time that he established the nearby St Nicholas' Church. de Lacy was relieved of his command of the town in 1210, when King John himself arrived and placed the castle under royal authority. de Lacy eventually regained his title of Earl of Ulster in 1227, however the castle and its walled town were captured several more times following his death (in 1242) and the town largely destroyed by the Scots in 1402.
The Battle of Carrickfergus, part of the 9 year was, took place in and around the town in November 1597. It was fought between the crown forces of Queen Elizabeth 1 and the Scots clan of MacDonnell, and resulted in a defeat for the English. A contemporary Elizabethan illustration of Carrickfergus shows ten tower-houses, as well as terraces of single-storey houses, some detached cottages and 70 or more Irish beehive-type huts in the town.
In 1912 the people of Carrickfergus turned out in their thousands to watch as the RMS Titanci make its first ever journey up the lough from its construction dock in Belfast. The famous passenger liner was anchored overnight just off the coast of Carrickfergus, before continuing on its journey.
In April 2001 there was a population of 27,201.