Kylemore Castle was built in 1868 as a private home for the family of Mitchell Henry, a wealthy doctor from London whose family was involved in textile manufacturing in Manchester, England. He moved to Ireland when he and his wife Margaret purchased the land around the castle, after having travelled there on their honeymoon in the mid 1840's. He became a politician, becoming an MP for County Galway from 1871 to 1885. The castle was designed by James Franklin Fuller, aided by Samual Ussher Roberts. The construction of the castle began in 1867, and took the total of one hundred men and four years to complete. The castle covered approximately 40,000 square feet and had over seventy rooms with a principal wall that was two to three feet thick. The facade measures 142 feet in width and is made of granite brought from Dalkey by sea to Letterfrack and from limestone brought from Ballinasloe. There were 33 bedrooms, 4 bathrooms, 4 sitting rooms, a ballroom, billiard room, library, study, school room, smoking room, gun room and various offices and domestic staff residences for the butler, cook, housekeeper and other servants. Other buildings include a Gothic cathedral and family mausoleum containing the bodies of Margaret Henry, Mitchell Henry and a great grand-nephew John Henry.
The castle remained in Henry's estate after he returned to England. The castle was sold to the Duke and Duchess of Manchester in 1903, who resided there for several years before being forced to sell the house and grounds because of gambling debts. In 1920, the Irish Benedictine Nuns purchased the castle and lands after they were forced to flee Ypres, Belgium during World War I. The nuns, who had been based in Ypres for several hundred years, had been bombed out of their Abbey during World War I. The nuns continued to offer education to Catholic girls, opening an international boarding school and establishing a day school for girls from the locality. The school acted as the main educator for most girls from Renvyle, Letterfrack and further afield for almost a century but it was forced to close in June 2010. The nuns have since been developing new education and retreat activities.
The Estate includes large walled Victorian Gardens. Since the 1970's these have been open for public tours and 'nature' walks. The Benedictine community has restored the Abbey's gardens and Cathedral with donations and local artisans in order to be a self-sustaining estate.