The name Portstewart is relatively modern and came into being from 1734 onwards when Alexander McDonnell, the 5^th Earl of Antrim, gave the lease of a boat slip and surrounding lands to the Stewarts of Ballylease, a branch of the Royal Stewart s and the same Stewarts that owned Ballintoy.

Like most of the north coast, where safe anchorage for fishing boats existed, small settlements grew up and eventually harbours evolved. The first settlers here would have been primarily fishermen and their families. After the lanldlord arrived, investments were made and the first purpose built harbour was constructed in1832, later in 1889 this was enlarged with the final harbour you see today being finished in 1910.

The estate itself was inherited through marriage by the Cromie family of Cromore demense and later through marriage to the Montagu family. The estate also included land which was adjacent to the Stewarts estate and at that time owned by the O'Hara family who built an impressive castle on the promantory where the Dominican College is today. The castle was bought in 1917 by the Domincan Sisters who founded the college, it was later extended and modernised and still functions as a college today.