The William H. Williams Papers, spanning the dates 1907–2006, comprise 11.6 linear feet of manuscripts, academic papers, correspondence, photographs, teaching materials, oral histories, and other sources relating to the research and writing of Williams, a prominent Delaware historian based in Sussex County, Delaware. The collection is divided into six series, with series III. through VI. corresponding to major subject areas studied by Williams.

Series I. contains Williams's personal documents. It includes his diplomas, correspondence (including letters from Williams's mentor and colleague, Delaware historian John Munroe), book reviews, lecture notes, and academic papers written by Williams, news articles regarding his activities, and an annoted copy of his 1985 book . It also includes slides of images used in his publications and classes, as well as slides of photographs taken by Williams personally. Much of the material in the series documents Williams's involvment with the University of Delaware Parallel Program and its evolution over the years. Included are minutes, memos, news articles, and correspondence to and from Williams and others on the subject of the Parallel Program, a two year Associates in Arts degree program offred by UD in conjunction with Delaware Technical & Community College, on the DTCC campuses in Wilmington, Dover, and Georgetown. The material documents various complications and difficulties faced by the program over the decades.

Series I. also documents Williams's involvement with the Delaware Humanities Forum and the local community. There are several awards received by Williams as well as material related to various causes, committees, and groups Williams was connected with over the years. This series includes transcripts of the 1976 Sussex County Oral History project, for which Williams served as project director, as well as short biographies of the interviewees.

Series II. contains articles, reports, and other documents relating to subject areas studied by Williams over the course of his career. This series includes many papers on topics of archeology, architecture, and the American frontier as well as material for History classes taught by Williams. There is information on the Pennsylvania Hospital, which was the topic of Williams's dissertation, and other medical instutions, as well as Delaware state statistics, information on the city of Wilmington, crime, Delaware politics, and transportation. Much of the information relates to historical sites in Delaware and includes images of these sites. There are also several resumes and biographical information collected by Williams.

Series III. contains material related to the environment and documents Williams's research towards his final book, . The majority of the material consists of news articles, environmental studies, soil assessments, weather statistics, academic reports, and other information relating broadly to humankind's impact on the environment in Delaware. The time period covered by the various works spans from prehistory to the present day. The series also includes three oral interviews conducted in 2004 by Williams on the subject of the environment and waste management. There are multiple drafts of (earlier titled "Neither Garden Nor Desert"). The book explores the history of humankind's interaction with nature in Delaware and focuses on the consequences to the environment starting with European colonization of the area in 1631. It covers the rapid growth of industry in the state and follows state and federal efforts to address the resulting environmental problems.

Series IV. contains material related to slavery, civil rights, and race relations in Delaware. It includes academic research, news articles, census records, teaching materials, and drafts of Williams's book . The aforementioned materials relate to the topics of slave ownership in Delaware, plantation life, and the population of slaves and free blacks prior to the American Civil War. The materials aslo concern the fate of blacks in Delaware after empancipation, race relations in Delaware, and the Civil Rights movement in the state. There are two drafts of Williams's book, one with annotations, and material related to the production of the book, such as image requests, reviews, and notes. Also included are a grant proposal, teaching packet, and video cassette of a 1997 WHYY television series, "Freedom's Edge: African-Americans in Delaware, 1639-1865," on the history of slavery in Delaware. The series was created with the help of Williams and University of Delaware professors Carol Marks and James Newton, and features a roundtable discussion in which Williams participates.

Series V. contains material related to Williams's personal and academic interest in Delaware Methodism. It includes material documenting his involvment in the Wesley United Church in Georgetown, Delaware, images of well-known Methodists, and reviews and correspondence regarding his book . Also included is information gathered by Williams on early African-American Methodism and Barratt's Chapel (Frederica, Delaware), the oldest surviving church built by Methodists in the United States. The material related to Wesley United Church demonstrates Williams's involvement in church leadership and administration. It includes meeting minutes, strategic planning something, and in the form of meeting minutes, notes, Also included are packets from the church's Vision Team, responsible for future planning and development, and the Nuturing Committee, tasked with encouraging spiritual growth within the community as well as welcoming new members.

Series VI. contains material related to the poultry industry on the Delmarva Peninsula. It includes news articles, poultry association profiles and studies, information about the University of Delaware's Cooperative Extension program, and research towards Williams's book . The bulk of the material consists of poultry industry (broiler industry) histories, annual growers' reports, industry newsleters, news articles, and production assessments. Much of this material was used by Williams to write his book on the poultry industry. Because of the effect of large scale poultry farming on the environment, there is also some overlap with his work on the environmental history of Delaware. Another topic covered by this series is the effect of migrant labor on the Delamrva poultry industry and it contains news articles on the topic of immigration. Related to this are articles and reports documenting controversy surrounding the working conditions at poultry plants. Also included are audio tapes of oral interviews conducted by Williams. The interviews involve discussions with poultry industry owners and employees regarding their experiences. Acccompanying the interviews is a notebook containing brief notes taken by Williams about the interviews and the backgrounds of the interviewees.

Taken as a whole, the collection documents Williams's personal and professional journey as a historian mining topics essential to an understanding of Delaware. Benefitting from his residency in Sussex County and familiarity with life "below the canal," Williams's research on the topics of race relations, religious heritage, agriculture, and the poultry industry, as well as the natural and environmental history of the state resulted in publications and research that greatly enhance an appreciation of the state.