After 1604, Sir Edward Blayney began constructing this fortified residence, resourcefully using materials salvaged from the town's former Franciscan friary. The castle doesn't appear on the Bartlett map of 1602-03, suggesting construction hadn't yet begun, but by the time a later map was drawn around 1611-13, now preserved in Trinity College Dublin, the castle stood complete within its defensive walls.

The Trinity College map reveals the castle's strategic layout: a rectangular bawn enclosed the main structure, with a northern gate providing controlled access and defensive bastions positioned at the northwest and southeast corners. South of the castle, within the protected grounds, formal gardens and fish ponds offered both sustenance and leisure for the inhabitants, typical amenities for a gentleman's residence of this period. These features paint a picture of a fortified yet comfortable home, balancing military necessity with the genteel aspirations of its Protestant planter owner.

By the 19th century, the castle had vanished from the landscape, though local memory persisted. In 1835, residents could still point to its former location on the Diamond, opposite Glasslough Street, likely indicating where the northern section of the bawn once stood. Despite archaeological excavations conducted in 1996 searching for traces of the castle to the southwest, no physical evidence emerged, leaving us to rely on historical maps and documents to imagine this lost piece of Monaghan's plantation heritage.