In the Hamlin Garland papers are more than 8,500 letters written to Hamlin Garland by almost 3,000 correspondents. There are also almost 1,700 letters written by Mr. Garland to some 650 correspondents. Of these latter, most are Garland's drafts are carbon copies, only about 350 being originals. Scholars will be especially interested in the collections of letters from Garland's many literary friends, especially those of major figures who were his intimates, such as James M. Barrie, Henry Blake Fuller, William Dean Howells, Henry James, and Theodore Roosevelt.

Some letters found in the correspondence files of the Garland papers were exchanged between two persons other than Garland. These are listed, and both correspondents are named in each records' title or scope and contents field. Whenever "Garland" is used without a first name, the description is referring to Hamlin Garland.

Many of the letters to Garland are addressed to "S. S. McClure" because Garland was a frequent contributor to McClure's Magazine and was sometimes reached via the magazine's offices.