Porter's unpublished manuscript, “Black Riders: The Negro on the Frontier of the Cattle Country,” 1953-1978 (11.6 lin. ft.), also the title of the subseries, is a study that examines the role of African Americans in the West - specifically in the cattle country, mining regions and dry-farming areas. Porter wrote about African-American cowboys and their relationships with American whites and Native Americans, in addition to African Americans who lived in the cattle country but did not work directly with cattle. These occupations included agriculture, transportation, service occupations, entertainment, general labor, business, the professions, journalism and public office. He discusses Jim Crow, African-American resistance, retaliation and accomodation, as well as the portrayal of the cow-country African American in literature and on the screen.

The collection consists of numerous drafts of Porter's manuscript for “Black Riders.” He had labelled the drafts “early version,” “outmoded version,” “late version,” etc. In processing the collection, these terms have been used but the material was not studied in sufficient detail to determine whether the arrangement of the versions is indeed in the order in which Porter wrote them. However, when possible, all of the manuscripts which pertain to each of the twenty-two chapters were kept together. The manuscripts are followed by reference material he compiled for each of the states he discusses; this material includes correspondence, notes and printed matter. Porter maintained a great number of notes on index cards; the titles he provided on these boxes have been retained. These notes have been placed at the end of the subseries relating to the particular subject. There are six such boxes for “Black Riders.”

“The Negro on the American Frontier” subseries, 1963-1973 (1.4 lin. ft.) is also the title of Porter's book which was published by Arno Press and The New York Times in 1971. This book is a collection of Porter's most significant published articles on African Americans on the American frontier, originally written over a period of thirty-seven years and newly edited and updated for this book. This compilation expands the study he prepared for “Black Riders,” and, in addition to African Americans in the cattle country discusses African Americans in other sections of the United States, the Seminole War, fur trading, the sodhouse frontier, etc. Material for this book includes Porter's research proposals, manuscripts, correspondence, reference articles and index card notes.

Seminole Manuscripts subseries, 1943-1978 (11.8 lin. ft.) includes manuscripts, correspondence, reference material, index card notes, reference articles written by other researchers as well as other articles published by Porter, and microfilm of government records primarily housed by the National Archives. Porter wrote about many aspects of Black Seminoles living in Florida, Texas and Mexico; wars with the United States; and war chiefs and leaders. Included in the subseries is the manuscript entitled, “Freedom Over Me: A Folk History of Wild Cat - John Horse Band of Seminole Negroes, 1849-1882.” This paper focuses on the Black Seminoles who settled in Northern Mexico in the early 1850's and returned to Texas in the early 1870's as scouts for the United States Army, and most particularly their chief John Horse, also known as Gopher John. Porter also conducted research into the second Seminole War which lasted from 1835-1842, as well as the time period which followed. Additionally, Porter did extensive research on two Seminole leaders, John Horse and Wild Cat (aka Coacoochee). The Black Seminoles took a leading part in resistance to the annexation of Florida and to the removal of Seminoles to Arkansas. When white men and Creeks began to capture and sell the Black Seminoles, John Horse, the Black Seminole Chief, led an exodus of Black Seminoles to Mexico in association with a similar movement of Indians led by Wild Cat, chief of the discontented Seminole Indians. Manuscripts for Porter's research about Billy Bowlegs, the Seminole Indian Chief, is also included in this subseries.

The subseries “Dictionary of American Negro Biography,” (.6 lin. ft.) consists of correspondence, research material and manuscripts for entries Porter either wrote or contributed ideas to, for this dictionary.

The General History, 1938-1980 (22.2 lin. ft.) consists of material that pertains to African Americans, Native Americans and general American and European history that cannot be identified as belonging to any of Porter's manuscripts. The type of material includes correspondence, manuscripts, research notes, numerous index card notes, news clippings, articles by other researchers, and Porter's published articles and book reviews. Included in this subseries is research material about Long Lance, the athlete of African- American and Native American descent, and material about slavery in addition to letters Porter wrote to editors and articles about African Americans. The folders entitled “African-American - Related Correspondence, 1970-1981” contain correspondence which was removed, after careful examination of each letter, from the Correspondence subseries of the “American and European Manuscript Research Material series.” Additionally, Porter's index card notes about African American, Native American and general American history have been placed in this subseries. Some of these notes were used in Porter's college teaching.

The Writings subseries, 1927-1980 (1 lin. ft.) includes Porter's Master's thesis, his published articles about Oregon business history and the fur trade, and transcriptions of letters Porter used in his book, The Jackson and the Lees, Two Generations of Massachusetts Merchants, 1765-1844, 2 vols. (Cambridge: Harvard University Press, 1937). There are also correspondence and drafts for the book he co-authored with H.M. Larson, History of Humble Oil and Refining Company: A Study in Industrial Growth, (New York: Harper, 1959). Manuscripts for articles about several historical figures are also included in this subseries.

The Folklore subseries, 1940-1978 (2 lin. ft.) consists of correspondence, research notes, manuscripts, book reviews, news clippings and other printed matter reflecting Porter's interests in American, European and Australian folklore.

Porter was deeply immersed in poetry and socialism, socialist issues and the writing and critiquing of poetry for half a century, beginning in the 1920's. The Correspondence - Poetry and Socialism subseries, 1926-1981 [bulk, 1930's-1950's] (4 lin. ft.) reveals the breadth of Porter's interests. His socialist correspondents include Arthur W. Calhoun, Bessie (Flora) Hurst, Naomi Mitchison and Bouck White. The following is a list of poets and literary figures with whom Porter corresponded: Colby Cleveland, Jack Conroy, Joy Davidman, Margaret Tynes Fairley, Truth Mary Hemenway, Rosalie Hickler aka Rosalie Boyce, John Holmes, Harry Elmore Hurd, Raymond Kresensky, Seymour Gordden Link, Ruben F. Menendez, Russell Porter (Kenneth's brother), Lou Agnes Reynolds, Edwin Arlington Robinson, Theodore Roethke, Julia Ruutila, Irma Wassall, and John Wheelwright. Researchers should note that many of these poets were also socialists, and socialism is frequently the focus of their writing. Porter prided himself on being a poet from Kansas, and a number of his colleagues also wrote about Kansas. As an admirer of Robert Frost, Porter wrote an article reminiscencing about his conversations with Frost between 1935-1936 and in 1941. This subseries contains Porter's research material and manuscripts about Frost as well as a 1935 handwritten letter from Frost to Porter. Also included is Porter's research material about Solomon de la Selva, a Nicaraguan poet. As a member of the New England Poetry Club, he maintained correspondence and issues of the newsletter. There are also additional letters about history, literature, folklore, and politics, some written by Porter's wife, Annette, as well as numerous letters to editors with the pertinent news clippings attached. Finally, there are numerous incoming letters and one folder of outgoing letters. Porter had arranged the incoming letters chronologically and indicated they had been answered; this arrangement has been followed. These are letters from colleagues and friends, many dealing with historical subjects.