The Sir William Osler Collection, distinct from the Bibliotheca, is an extensive archival holding of Osler's correspondence (including eighteen hundred original letters), daybooks, accounts, engagement books, legal documents, book invoices, membership certificates, notebooks, lectures, addresses, newspaper clippings, photographs, books with manuscript additions, and miscellaneous loose items formerly inserted into individual books in his library. The collection also contains various family papers, including correspondence of Lady Grace Revere Osler and Edward Revere Osler.

Fonds documents the Mallochs' activities related to their medical and literary work. The fonds contains notes, correpondence, commonplace books, account books, material related to publications, family memorabilia, scrapbooks, photographs, telegrams, postcards and certificates.

The fonds contains Dr. Jacques' journal of medical accounts receivable entered in an account book issued with blank pages and bound in half suede with green cloth boards. The account book was kept between November 1879 and January 1881. A title handwritten on a paper label on the cover reads "Journal pour 1879-1880-1881." The author's full name comes from within the journal (L. A. George Jacques, M. D.) and from Lovell's Montreal directory for 1881-1882 (Louis A. George Jacques, M. D.). Laid in at p. 207 is an ink blotter featuring pharmaceutical advertising for Glyco-Heroin (Smith).