The site sits on a low rise of rock outcrop at a place called the Island, where a small watercourse known as the Maudlin River joins the Barrow from the south. The association with Dermot MacMurrough, the twelfth-century King of Leinster whose invitation to the Anglo-Norman Richard de Clare, known as Strongbow, effectively opened Ireland to the Norman invasion, turns out to rest on uncertain ground. Scholars believe the connection arose from a misreading of the Latin phrase 'de insula', which refers more plausibly to Great Island elsewhere in Wexford than to this particular stretch of river bank.

The documentary record that does attach to this place is more modest, though not without colour. In 1537, one Cahair McArt of Macmurroughs Island led an attack on the nearby town of Fethard at the urging of John Purcell, Bishop of Ferns, plundering twenty of the inhabitants and driving off 115 cattle, some of which apparently belonged to the bishop himself, and which His Lordship subsequently and quietly recovered. By 1641, according to the Civil Survey of 1654 to 1656, sixty acres at the Island in the Liberties of Ross were in the hands of Edward Fitzharris, described as an Irish papist, though the survey makes no mention of any castle standing on the land. Excavations carried out by C. Cotter in 1985 and again between 1986 and 1987 uncovered the remains of a rectangular building measuring roughly 14.5 metres east to west, its walls of faced drystone construction, probably occupied no earlier than the seventeenth century. Prehistoric material, including a stone axe and worked flints, also came to light in disturbed contexts, suggesting human activity on the rise long before any named family claimed it. The building itself no longer exists in any accessible sense; it now lies beneath the N30 road between New Ross and Enniscorthy, sealed under tarmac rather than soil.