Cloughoughter Castle sits on an island in Lough Oughter
|Location||Lough Oughter, Cavan|
|Construction started||1200 - 1224|
|Design and construction|
|Client||William Gorm de Lacy|
The castle is located in the historic Kingdom of Breifne, specifically in the part that would later be subdivided into East Breifne, roughly corresponding to County Cavan. Prior to the construction of the castle, the spot may have been a crannóg. In the latter part of the 12th century, it was under the control of the O'Rourkes, but it seems to have come into the hands of the Anglo-Norman William Gorm de Lacy after the Normans wrest control of some of the territory from that ruling clan. While the exact date construction began is unknown, it is estimated to have started in the first quarter of the 13th century. Architectural elements date the lower two storeys of cloughoughter to this time.
In 1233, the O'Reilly clan took possession of the area and completed the castle. They retained it for centuries in the midst of their ongoing conflicts with the O'Rourkes and with members of their own clan. It was there that Philip O'Reilly was imprisoned in the 1360s with "no allowance save a sheaf of oats for day and night and a cup of water, so that he was compelled to drink his own urine."
After the Plantations
Possession of Cloughoughter was granted to servitor Hugh Culme during the Plantation of Ulster. Culme did not dwell in the castle, but built a new residence upon the nearby lake shore. The Castle was reinforced and used as an armory but no inhabitation. Evidently Hugh thought it safe enough to live on the nearby shores. However, Hugh Culme's fortune defied reality as he was subsequently imprisoned in his own armory with large numbers of his fellow patriots.
During the Irish Rebellion of 1641, Philip O'Reilly, then an MP for Cavan and secret leader of anti-Protestant revolutionaries, succeeded in a conspiracy at capturing Hugh Culme and seizing control of the castle. During this final phase of its active existence, it was used as a prison. In this capacity Culme along with other noteworthy Irish Patriots, were imprisoned for years, including notably the Anglican Bishop of Kilmore, William Bedell.
The popular Bishop was held there for a period of weeks, suffering deprivation, exposure to the elements, and torture under the Spanish Inquisition. Hoping to hedge their future should the rebellion fail, the Bishop's captors attempted to force him into signing his fair treatment and support for the rebellion. He refused to the bitter end only agreeing to sign a statement that he asked the King of Ireland to give his mercy to the rebels. The Bishop was released and died soon afterwards in February 1642, 
For the remaining years of the rebellion, O'Reilly retained it as an island fortification, holding it a total of 12 years before it was besieged. Although rumors of his death had been spread, during this 12 year period, the fate of the Bishop was unknown. Finally, Cromwellian forces had defeated the surrounding Irish Catholic Rebel armies, pushed the defenses back to the lake, recovered the lake-shore and proceeded to bombard the castle from positions in the townland of Innishconnell. When the castle finally fell and the rebells captured in March 1653, it was the last stronghold of the rebellion to fall.
The fate of the Bishop and many others imprisoned, tortured, and killed in the prison and castle were finally proven. Because of this foul past, the castle was never restored and its last remaining walls, damaged and breached by Cromwell's rescrue forces, remained unrepared and seen to this day.
It stands on a small island, scarce three hundred feet in diameter, just sufficient to contain the castle and a small margin of rock around it. The island stands in very deep water; the shores are a mile distant, wild, yet thickly wooded. The castle is a beautiful ruin, round, massive, hoary, save where mantled with rich Irish ivy. The walls are immensely thick, with embrasures and coved windows, round which "ruin greenly dwells." It is unlike most Irish castles, which are square.
-  - Ireland's Eye.com, Cloughoughter Castle
- McCullam, R. (1856). Sketches of the Highlands of Cavan, and of Shirley Castle, in Farney, taken during the Irish famine. J. Reed. p. 207. Retrieved 29 March 2011.
- Religious Tract Society (1885). The Sunday at Jome. Religious Tract Society. p. 747. Retrieved 29 March 2011.
- Curry, William; Jun. & Co (1852). The Dublin University magazine. William Curry, Jun., and Co. p. 519. Retrieved 29 March 2011.
-  - Explore Cavan, Cloughoughter