Ownership, meanwhile, of both the castle and the lands upon which it stood had passed from FitzGearld into the hands of another local landlord called Chandley. Sometime about the middle of the 18th century, Chandley leased Mountain Castle and 64 acres of land surrounding it to the O'Keeffe family. What remained of the castle was roofed and converted into what must have been a grandiose farmhouse with two extensions to the original structure forming two new wings. It was to remain in the hand of O' Keeffe family for the next two hundred years. A letter written by the a relative of one of the last of the O'Keeffes to live in Mountain Castle in 1931, gives details of the dining room with its huge walnut beams, the circular nursery and marble fireplaces valued at $5000. Egan in his guide to county Waterford in 1895 describes Mountain Castle as 'the beautiful residence once occupied by 'John O'Keefe, Ballylemon Lodge.'
The O' Keeffe's, it would seem started out in the beginning or middle of the 18th century as medium-sized tenant farmers at Mountain Castle. By the middle of the 19th century, it is clear that various branches of the family had accumulated between them a moderate amount of land locally which they either owned and leased or leased themselves from landlords and subsequently sublet to smaller tenants. Like so many native landlords, however, the O'Keefes were far from benevolent as is apparent from events which occurred in 1838, two years before the beginning of An Ghorta Mór, The Great Famine:
'... 1838 witnessed the killing of that extremely tough land distributor John O'Keeffe of Mountain Castle. O'Keeffe, a catholic, who had risen 'from a low origin' and was described as 'upwards of 80 years of age', had scant respect for tenants rights. He was not in the habit of giving rent receipts and moreover if a tenant improved the land O'Keeffe simply raised the rent. It appears the decision to evict the Tobins of Lyreattin [ a local townland], who refused to pay an increased rent having improved their holding, together with O'Keeffe's purchase of the lands of Ballykerin [another nearby townland] ... finally provoked the community from which he had sprung too far. Both existing and prospective tenants had enough. Although O'Keeffe survived the assassination attempt on 4th April 1838 when a pistol shot went through his coat, he received a blunderbuss when he rode to Mass at Modeligo on Sunday May 1838 and died from his wounds 10 days later.'
Despite of or in testament to the ruthlessness of the O' Keeffe's as landlords, John O'Keeffe's grandson, also called John and who resided in Ballylemon Lodge near Dungarvan, was elected M.P. for Dungarvan in 1874, dying before the next election of 1880.
The last of the O'Keeffe's to live in Mountain Castle died in the early 1930's. The house was gradually allowed to fall into decay through years of neglect. It was subsequently owned by a local family, the Walshes, whose descendants are now the proprietors of the Mill House nearby in Millstreet, before being purchased by a James Doocey who later sold the house and land to speculators in the early seventies. It was purchased in 1973 by Joan and Emmet Nugent who went about restoring and repairing as much as possible the damage the house had endured over the years. They opened the house to the public as a guest house for the first time in 1978 under the name of Castle Farm.