The Castle is a State Care Historic Monument in the townland of Dundrum, in Newry, Mourne and Down District Council area, at grid ref: J4047 3700.

[2] De Courcy's original castle may have had defences of earth and timber, but the stone curtain wall of the upper ward was probably built at the beginning of the 13th century.

Hugh de Lacy strengthened the castle with a massive round keep, probably employing master masons from the Welsh Marches, where such keeps were then popular.

[3] Although much of the second floor of this keep was rebuilt in the 15th century, it is clear from the survival of the old fireplace flue and spiral stair that it originally stood at least three storeys high.

The stone curtain wall of the outer bailey is likely to have been built by the Mac Artáin chiefs of Kinelarty, who owned Dundrum in the late 15th century.

Dundrum House served as the home of Cornelius Maude, Viscount Hawarden and his descendants until the early 20th century when the structure was sold to an order of Roman Catholic nuns.