The collection consists of documents, correspondence, photographs, and other papers of William Courtenay (1832-1901), an English settler, veteran of the American Civil War, and frontier businessman who held positions in the United States Department of the Interior as postmaster, clerk, and Indian Agent at Fort Berthold, Dakota Territory, from 1874 to 1882. These materials provide insight into the daily happenings and systemic issues at the Fort Berthold Indian Reservation, and are of particular interest for their documentation of frontier transactions, corruption and mismanagement within the reservation system, and the relationships between the people of the Three Affiliated Tribes, the Sioux people, and white settlers during the late 19th century.

Materials created by Courtenay span from 1850 to 1897, though most date to Courtenay's years at Fort Berthold. Initially a fur trading post and then an army outpost, Fort Berthold became the Indian Agency for the Three Affiliated Tribes, the Mandan, Hidatsa (also referred to in these documents as Gros Ventre), and Arikara, in 1868. It was made part of the Fort Berthold Indian Reservation in 1870, but the United States government flooded the fort's original site when they constructed the Garrison Dam in 1947-1953 and destroyed the traditional grazing and hunting lands of the indigenous population. This portion of the collection is notable for its documentation of conditions at Fort Berthold in the 1870s and 1880s from the perspective of indigenous inhabitants. Highlights include an eight-page report with testimony by Gros Ventre Chief Lean Wolf (also known as Chief Poor Wolf) relating to poor treatment of Native Americans and Sioux violence; a series of letters from Gros Ventre Wolf Chief to William Courtenay and his wife discussing his people's poverty, distrust of a new Indian Agent, and other struggles, many due to corruption by government agents. Additional perspectives can be found in Courtenay's postmaster letterpress copybook, which details activity at Fort Berthold and contains additional accounts of corruption and theft of provisions by white families. Documents in this collection attest to the fact that the Three Affiliated Tribes suffered greatly at the agency due to inadequate military protection, violence from the Sioux people who distrusted the Mandan, Hidatsa, and Arikara due to their history of cooperation with white settlers, meager food rations, and the corruption of government officials and traders.

Courtney's personal papers include photographs, additional correspondence with family members and others, poetry and other narrative writings that often reflect on his travels and professional career, legal documents, clippings, ephemera, and lists and catalogs related to his collection and sale of Native American cultural objects, many of which he acquired from Fort Berthold. There are also a small number of later materials dating from after Courtenay's death in 1901 to 1965 which were added to the collection by family members who were researching Courtenay's life. These include genealogical writings, letters, and printed materials about Courtenay that were collected by members of the Terrett family.