Deel Castle, Tower house ruin in County Mayo, Ireland

Deel Castle is a tower house ruin located near the northern end of Lough Conn in County Mayo. The structure consists of a medieval rectangular tower and the remains of an additional wing built in the 18th century.

Deel Castle was built in the 16th century by the Bourkes as a tower house near the northern end of Lough Conn. After Colonel Thomas Bourke fought for King James II & VII in the Williamite Wars, the property was forfeited and granted to the Gore family, later Earls of Arran, who renamed it Castle Gore. In the 18th century a large wing with a rusticated doorway was added, possibly incorporating a 17th-century range. The castle was leased to James Cuff, Lord Tyrawley, in the late 18th century and later fell into ruin.

The Irish name Caisleán na Daoile means "Castle of the River Deel", taken from the watercourse the tower house was built beside. The Gores renamed it Castle Gore after acquiring the forfeited Bourke estate, and the older Irish name survives alongside the later English one.

The site shows building remains from different time periods, including a rusticated doorway and traces of both medieval and 18th-century construction. When visiting, be prepared for uneven ground and the exposed structures that have survived the elements.

A separate house built beside the castle in 1791 was once a distinct landmark of the area. It was destroyed in 1922, leaving only the original tower structure visible today.