Having summered there since 1933 when his mother and then he rented the castle, McIlhenny purchased Glenveagh in 1938 from the widow of Harvard art historian A. Kingsley Porter. According to documentation in this collection, McIlhenny purchased, for approximately $25,000, a 19th-century, 23-bedroom castle with some of its contents and other buildings situated on more than 25,000 acres of land in an area not far from the birthplace of his grandfather, John McIlhenny. When not in Ireland, McIlhenny stayed informed through constant correspondence with his agent in residence as well as with a local solicitor. Correspondence with most of the men who served as McIlhenny's agent begins the subseries. The bulk of these writings were generated by Julian Burkitt, who held the position from 1955 until 1980, at which time he also assumed the role of superintendent of the Glenveagh National Park. The latter position, which Burkitt held until 1985, came about from McIlhenny's gift of the castle and grounds to the Irish government.
Burkitt's letters with McIlhenny offer vivid and detailed accounts of a working country estate. Discussions of livestock and deer, comments on the weather and sketches of proposed construction, such as a machinery building and byre, are among Burkitt's topics, as are updates on the gardens, greenhouses, and various repair projects. His reports on the staff occasionally contain snippets of human drama, such as the young gardener's secret departure for Scotland with a girl, which left his family "much perturbed." Burkitt's correspondence with McIlhenny's Philadelphia secretary is also included and pertains primarily to paying employees and local businesses, giving an idea of the type of goods and services needed to maintain such a productive estate. In the years preceding Burkitt's tenure, J. Allan Osborne, solicitor of Osborne & Co., gives similarly detailed and descriptive accounts in his letters to McIlhenny. In these files of correspondence, which follow the agent folders, Osborne reports and advises on numerous issues, including McIlhenny's purchase of the estate, the hiring of staff and other workers, and the earliest renovations and repairs made to the castle as well as to other buildings on the grounds. From 1939 to 1946, Osborne's commentary is particularly significant since the war prohibited travel and McIlhenny's naval commission continued to keep him stateside. Moments of melodrama also appear in a few of Osborne's letters, beginning in the fall of 1940, that pertained to McIlhenny's first agent who was brought to court years earlier on charges of seduction. Because of counter-charges of harassment and ensuing he said/she said accusations, the matter continued to appear in Osborne's letters until as late as 1952, as well as in the correspondence of others, and in the local newspapers. Two types of statements generated by Osborne & Co. follow the firm's correspondence. Itemized cost and expense statements detail the services provided by the solicitors. The estate accounts record expenses incurred in the maintenance and operation of the estate and monies coming in to offset the costs.
Most of the remaining files are identified by the subjects documented, with material comprised primarily of correspondence and invoices. These subject titles were assigned during processing. Several items belonging to the previous owner are also included and made evident by folder title or pre-1938 date. The "Employee" and "Wages" files identify the household staff and are best supplemented by many of Burkitt's descriptive letters as well as some of the "Bookkeeping" records in the "Financial" series. Although material in the "Art collection" series documents most of the purchases McIlhenny made to furnish Glenveagh, the "Interior decoration" folders in this subseries also give an idea of the castle's furnishings, including orders for wallpaper, paints, window treatments and floorings, as well as a few articles of furniture and upholstery work. Most of the "Home maintenance" files deal with utilities and large applicances. The ephemera accompanying the kerosene refrigerator that McIlhenny bought in the U.S. for his castle vividly illustrates modern technology and design of the late 1930s. Several of the drawings included in the "Renovation" folders pertain to some of the other structures at Glenveagh. The old police barracks was remodeled for the estate agent's use for those months McIlhenny occupied the castle. Because of its location near a bridge, the barracks was also referred to as the "Bridge House." The cottage in the glen was redone for McIlhenny's sister and her children to use during their summer visits.
The "Property" folders primarily document the various transactions concerning the estate, beginning with the lease McIlhenny's mother took prior to her son's purchase. The next set of folders pertains to McIlhenny's purchase of Glenveagh, followed by documentation of his two-part "sale" and "transfer." Between 1974 and 1975, McIlhenny came to an agreement with the Commissioners of Public Works to sell most of his land to the Republic of Ireland for the creation of a national park. Then in 1979, McIlhenny made a gift of the castle and 15 surrounding acres, but retained the right to live there until 1982. (His last summer at Glenveagh was in 1983.) Several documents, as well as correspondence with various State officials and with McIlhenny's attorney, H. Ober Hess, pertain to these later transactions. A list of improvements gives a detailed description of buildings and other property features McIlhenny financed, while Sotheby's valuation of furniture, furnishings and works of art that were to remain in the castle suggest its furnishings when he lived there.
The "Photographs" folders attest to the spectacular views afforded by McIlhenny's 25,000-acre retreat, including the meticulously designed gardens and greenhouses. Several folders pertain to photographs used in magazine articles featuring Glenveagh. Casual outdoor shots of McIhenny are also included. Included in the "Other" files are papers related to the dance festival the former owner, Mrs. Porte,r held annually at Glenveagh. The final set of folders pertains to the Dunlewy property, which McIlhenny purchased in 1943. Although McIhenny paid for a staff and renovation work, it does not appear that he ever stayed at Dunlewy before selling it in 1952.