Although the Hellfire Club was founded at West Wycombe, England in 1741 by Sir Francis Dashwood, the Earl of Rosse, Richard Parsons, founded in 1735 an Irish branch--or perhaps it should be said that Dashwood's group was a branch of Parsons'. The Irish Club acquired for themselves, at least according to popular rumor, the house built on Montpelier Hill southwest of Dublin by William Connolly. Interestingly, Montpelier Hill was home to a caern and standing stone, both of which were destroyed during the construction. Author Weston St. John Joyce says that:

...it is to be observed that while the Hell-Fire Club may have held some of its meetings in this house, it is tolerably certain that it was never one of the regular meeting-places of that mysterious and iniquitous body, the ordinary rendezvous of which was the Eagle Tavern on Cork Hill.

At some point, the house caught fire and burned. According to one legend, recounted on the website of the restaurant currently located in Killakee House at the base of the hill, the fire was in 1740, and was the doing of "Burnchapel" Whaley. According to the story, a servant had spilled a drink on Whaley. "Burnchapel" had the servant doused in alcohol and set ablaze. The resulting fire killed many Hellfire Club members.

Other undesirable activities were associated with the Club, including the burning alive of a black cat on at least one occasion, the worshipping of cats in place of Satan himself, the setting ablaze of a woman stuffed into a barrel, and the beating and murder of a misshapen dwarf shortly before 1740. Parsons was a central figure in all the Hellfire Club's debaucheries.

Killakee House itself seems to be a focus for violence and mysterious phenomena, perhaps stemming from the Hellfire Club's activities or the destruction of the caern. In the early 20th century, Constance Markievicz, the "Red Countess" and first woman elected to the House of Commons, resided at the house. Markievicz took place in the Revolution of 1916, and during her stay there a gunbattle killed five members of the newly-formed IRA.

The 1960s saw the movement into the house of an art center, and it was this time which saw the dawning of the events for which Killakee is most famous. Upon moving to the house, the art center's employees heard legends from the locals of a huge black cat, legends which dated to 1918. The owner, Margaret O'Brien, did indeed see on several occasions some "big black animal." But it was artist Tom McAssey who had the most famous sighting of the Black cat of Killakee in March, 1968. After the front door had mysteriously unlocked itself, he saw a large black cat lying outside. McAssey said the cat spoke to him, saying "You don't see me." And then, when he tried to lock the door, "Leave this door open." (McAssey painted a picture of the cat, which has an eerily human face.)

O'Brien encountered many other, less exotic, ghostly phenomena at the house, many of them poltergeist-type in nature. She called in a Catholic priest to perform an exorcism, but to no avail. the hauntings continued. Finally, in 1970, a dwarfish skeleton was discovered under the kitchen floor, lending credence to the legend associated with the Hellfire Club. In the grave with the dwarf was a brass statuette of a demon. The priest was called a second time and the body properly buried. The manifestations stopped.