Covering the last decade of his life, this correspondence primarily documents McIlhenny's extensive social activities and the numerous friendships he cultivated in America and abroad. Many of the letters pertain to an exchange of invitations to dinner parties, cultural events, and vacation rendezvous, along with follow-up thank you notes. There are also numerous letters of thanks from McIlhenny for the many gifts he'd receive, ranging from a duck door knocker and jar of Col. Biddle's curry powder to having a star named after him as a Christmas gift in 1982. Knowing his interest in horticulture, long-time friends, such as Walter and Lee Annenberg, often sent plants and flowers. Based on the number of times received, orchids were McIlhenny's favorite. He also apparently enjoyed receiving cookbooks, and various foods, such as caviar, which he claimed to be his "favorite dish," and chocolate mints, which he described as his "fatal weakness." A number of museum colleagues and art dealers often sent McIlhenny exhibition catalogues, while other friends and acquaintances would send newspaper and magazine clippings, usually regarding Glenveagh. Letters written by McIlhenny's secretary informing correspondents of his death in the spring of 1986 are included as well as letters of condolence, including a photocopy of a telegram sent by President Ronald Reagan to the Philadelphia Museum of Art.
Some correspondence refers to McIlhenny's art collection and various organizational affiliations. Most are general inquiries and solicitations, or a mix of business with long-standing friendships. In both cases, appropriate cross-references were made. Some papers were transferred to other series. The only correspondence too numerous to cross-reference or transfer were requests to see or to borrow works of art from McIlhenny's collection. Almost every folder contains at least one visitor's request. The loan requests are less frequent, and McIlhenny refused most. (The many requests to which McIlhenny did agree are in the "Art collection" series). McIlhenny's personal letters of thanks to various individuals for their contributions to the Philadelphia Museum of Art are also included. The four folders at the end of the subseries each consist of multiple correspondents. "Australia" consists of thank you and other follow-up letters McIlhenny wrote upon return from his 1978 vacation down under. The letters in the "Thank you" folder are to friends identified by first name only. Most of the "To whom it may concern" correspondence pertains to employees of McIlhenny. The signatures to letters in the "Unidentified" folder were indecipherable.
The use of general alphabetical folders reflects the original filing system, as does the combining of "Philadelphia" and "Ireland" correspondence. During processing, however, any correspondent represented with at least ten items was filed individually.