The collection consists primarily of documents created or compiled by Lewis A. McArthur, particularly papers relating to McArthur's work on Oregon place names. The bulk of materials relating to Oregon place names consists of correspondence, notes, and newspaper clippings, including a few documents added after McArthur's death by Oregon Historical Society staff. Additional materials on Oregon place names include a complete final draft of the first edition of Oregon Geographic Names, a correction copy of the first edition of Oregon Geographic Names, and three bound volumes of correspondence.

Other papers in this collection consist of personal correspondence, articles and reports written by McArthur, and research McArthur conducted about Oregon post offices and postmasters. Family papers include correspondence and land papers of Lewis A. McArthur's father, Lewis Linn McArthur (1843-1897); and the papers of Lewis A. McArthur's brother Clifton Nesmith McArthur (1879-1923), including a letter from Theodore Roosevelt offering condolences for the death of Clifton N. McArthur's son.