Over a period of more than 55 years, three personal secretaries maintained Henry P. McIlhenny's files, resulting in different filing systems and retention practices. While the earliest secretarial assistant kept individual files for each correspondent and retained only certain invoices, her successors filed correspondence in general alphabetical order and kept what appears to be almost all invoices and/or receipts, also in general alphabetical order. In preparing the catalog for its 1987-1988 exhibition of the McIlhenny collection bequeathed to the Philadelphia Museum of Art, curatorial staff made significant use of relevant portions of the papers, which probably led to further rearrangement.

The designated series reflect categories that were imposed earlier and in varying degrees to the papers, arranging material by document types and topics. "Correspondence," "Financial records," "Family records," and "Articles, interview and lectures" make up the four material-type series. The three topical series that follow reflect the areas of McIlhenny's lifestyle for which he was best known, namely his "Art collection," his "Residences," and his "Affiliations" with the many organizations and institutions that benefited from his generosity and expertise. The final series, "Other subjects" encompasses smaller groupings of topical material, namely "Social events" and "Travel." The "Various" subseries houses other subjects and document types.

Because of the large amount of invoices, retention guidelines were established to insure that research value would not be jeopardized while maintaining practical and efficient processing standards. While some invoices pertain to the late 1930s, most date from 1960 to 1986, and the amount of information contained therein varies.

The significance of McIlhenny's fine and decorative art collection requires the retention of all relative invoices, regardless of amount of information. In keeping with the organization of earlier purchases (most of which were made by his parents), later invoices for all books and for jewelry have been added to the "Art collection" series. The other category of invoices retained entirely pertains to horticulture and therefore includes all gardening and landscaping expenses, as well as florist orders.

In assessing the remaining invoices, the first criterion was that there be some degree of detail, such as an itemized bill. The account books processed in the "Bookkeeping" subseries of the "Financial record" series offers the same information that can be gleaned from invoices showing only total dollar amounts. Itemized invoices retained were those documenting the more routine aspects of a privileged lifestyle, such as clothing, groceries, and health and beauty aids. Because only itemized invoices have been retained, the material must be studied as a sampling of such expenditures. All these invoices are part of the "Various" subseries in the "Other subject" series. Itemized invoices pertaining to interior decoration and renovations in Philadelphia and at Glenveagh have been processed in the respective subseries of the "Residence" series. In keeping with the original arrangement of earlier dated material in the "Philadelphia" subseries, later invoices pertaining to maintenance and repair, security and utilities were also retained.