The castle’s story begins with Sir Edward Blayney, an English garrison captain who arrived in Monaghan town in 1602. After proving instrumental in fortifying the town and building a defensive house there, Blayney received a grant of land at Ballylurgan (also called Ballifort) in 1607, on the condition that he construct a fort within four years. The strategic location, halfway between Monaghan and Newry, would serve as a secure stopping point for supply routes between the two towns. By 1612, Sir Edward had accumulated substantial holdings in Cremorne barony, potentially controlling seven of its twenty-two ballybetaghs, and in 1621, his success was recognised when he became the first Lord Blayney.

The castle Sir Edward built was an impressive fortification for its time. A contemporary account describes a substantial bawn; a defensive wall of lime and stone standing 18 feet high, complete with flanking bulwarks. The complex featured a grand gatehouse and two corner houses, each containing several rooms with chimneys, whilst within the bawn walls, construction had begun on an ambitious stone house with remarkably thick walls and vaulted ceilings. However, this promising stronghold met a violent fate in 1642 when local MacMahon rebels seized and ransacked the castle, possibly inflicting damage so severe that it never recovered. The estate changed hands several times over the following decades, passing through the Vincent family before returning to the Blaneys through marriage, though financial difficulties plagued the property throughout.

By 1770, when artist Francis Grose captured the castle in his drawings, it stood as a picturesque ruin; a T-shaped structure of two storeys plus attic, featuring distinctive Scottish-style corner machicolations supported by continuous corbels. The old castle’s exact location remains somewhat uncertain, though according to Charles Coote’s 1801 account, the replacement house (confusingly also called Castleblayney Castle) was built adjacent to the original ruins in 1799. This Georgian mansion, designed by Robert Woodgate, eventually passed to Henry Thomas Hope of Surrey in 1853 when the twelfth and final Lord Blayney sold the estate, and has been known as Hope Castle ever since.