The Cyrus Lawrence Day papers contain Day's research, notes, correspondence on topics of interest, and a draft of his book, Quipus and Witches' Knots: the Role of the Knot in Primitive and Ancient Cultures. Within some folders, when applicable, photocopies of the original folder have been provided to preserve any notes that Day had made on the front of his original folders. The original folder names have been used when available. This collection has been divided into two series.

Series I. Research contains material gathered by Day relating to his research interests in knots. This series contains two subseries. Subseries A. Articles, Notes, and Related Correspondence contains research materials collected by Day. The folders, organized by topic, consist of a variety of journal articles, notes about his research, or on particular articles, photographs, sketches, and correspondence. The material has been kept in the original order imposed by Day. Not all of the material is in English. Subseries B. Illustrations and Photostats contains a folder that Day labeled "Illustrations" which contains illustrations, photographs, notes about images, articles, and research notes. This series also contains photostats of images, some of which appear in the book Quipus and Witches' Knots: the Role of the Knot in Primitive and Ancient Cultures. There are also page proofs of the photostats.

Series II. Original Work contains typescripts and handwritten versions of Day's original work. This series includes early versions of the first three chapters of the book Quipus and Witches' Knots: the Role of the Knot in Primitive and Ancient Cultures contains, in addition to the completed manuscript with Day's edits and illustration. This series also contains handwritten and typed appendices of another of Day's works, Quipus Magic Knots and Surgeon's Slings. It is unclear if this was the start of another work, or if this was originally the name of some other work of Day's.