The Tom W. Reilly Collection consists of research materials, articles, and book drafts written by Reilly. These materials include Mexican War-era newspapers and correspondence, newspaper clippings, notes, photocopies of Villard and Garrison family correspondence, and several secondary sources relating to Reilly’s other areas of interest. The collection is divided into seven series: Biographical and Personal Files (1968-1992), Professional Files (1962-1999), Master's Thesis - Henry Villard: Civil War Journalist (1858-1986), The Mexican War (1829-2000), Personal Rare Manuscript and Publications Collection (1744-1995), Magazine and Newspaper Clippings (1857-1992), and Non-Manuscript Material (1876-1987). Each of these series is further divided into subseries according to subject matter and/or the administrative activities of the organization concerned.

Series I, Biographical and Personal Files, contains material regarding Reilly's time in the Peace Corps, his sabbatical year in China, and personal correspondence. Files are arranged alphabetically.

Series II, Professional Files, consists of materials related to Reilly’s professional activities, including his tenure at California State University, Northridge (CSUN), publications, and professional associations. This series is divided into four subseries: Subseries A: California State University, Northridge General Files (1968-1992), Subseries B: Journalism History (1974-1999), Subseries C: Publications (1970, 1974, 1987), and Subseries D: Professional Associations; Association for Education in Journalism (and Mass Communication), History Division (1962-1981). Records contained in this series include correspondence, newspaper clippings, and memoranda produced at CSUN; administrative records, editorial files, submissions, and book reviews from Journalism History, for which Reilly was founding editor; papers written by Dr. Reilly; and papers Dr. Reilly presented at the Association for Education in Journalism's annual conferences. The files are arranged alphabetically.

Series III, Master's Thesis - Henry Villard: Civil War Journalist, consists of materials relating to Reilly’s master’s thesis, Henry Villard: Civil War Journalist (University of Oregon, 1970). This series is divided into two subseries, Research Files (1858-1986) and Drafts and Associated Articles (1969-1972). Files consist primarily of research materials, papers, and articles based on his research, including a draft of his thesis project. Among the research files are numerous photocopies of Villard and Garrison family correspondence, as well as some directed to or from the NY Tribune, Mr. Villard’s employer. Files are arranged alphabetically.

Series IV, The Mexican War, consists of research materials and draft copies of an unpulbished manuscript dealing with the American War Press during the Mexican War. This series is divided into five subseries: Subseries A: Biographical Files of Mexican War Correspondents (1829-1998), Subseries B: Mexican War Newspaper Files (1843-1996), Subseries C: General Mexican War Research Files (1841-2000), Subseries D: Manuscript Drafts (1845-circa 2000), and Subseries E: Associated Articles and Publications (1973-circa 1999). The series includes biographical files of Mexican War correspondants, which consist primarily of correspondence, articles and book excerpts; newspaper clippings from American and Mexican newspapers during the war years, 1846-1848; and Reilly's research files on the Mexican War. The files are arranged alphabetically.

Series V, Personal Rare Manuscript and Publications Collection, is composed of rare items collected by Reilly dealing with diverse topics of interest. This series is arranged alphabetically by author or title of publication.

Series VI, Magazine and Newspaper Clippings, consists of clippings collected by Reilly. This series has been divided into two subseries, Clippings (1968-1992) and Full Pages (1857-1992). These materials  are arranged alphabetically by author/title where known.

Series VII, Non-Manuscript Material, includes audio materials, ephemera, microfilm, photographs, and transparencies.