The Denise O'Brien papers date from 1964 to 2007 and measure 15.2 linear feet. The papers are arranged in ten series, Biographical and family, Community involvement, Conferences, Correspondence, Organizational involvement, Resource files, Writings, Photographs, Artifacts, and Audiovisual.

The Biographical and family series contains biographies, awards, resumés, an appointment book, and passports. In addition to O'Brien's schoolwork, English papers, a class reunion booklet, and newspaper clippings, the series includes sporadic farm records and correspondence with Briana Harris, who attended Macalester College in St. Paul, Minnesota. Information about her experience with Hurricane Mitch can also be found in this series.

The Community Involvement series concerns O'Brien's activities with the United Methodist Church, the Atlantic School District, the PTA, her work with the Family Crisis Support Network in Atlantic, and files from her unsuccessful campaign for a seat on the Atlantic School Board. It also includes materials concerning school children's tours of the Harris-O'Brien farm. Information from her 2006 campaign for Iowa Secretary of Agriculture can be found in the sub-series, Campaign for Iowa Secretary of Agriculture. Along with fundraising and budget reports, newspaper clippings about O’Brien’s campaign, major talking points from her candidacy, information about her opponent Bill Northey, and the 2006 election results are also included in this sub-series.

The Conferences series consists of notes, programs, nametags, and other materials that O'Brien collected at local, national and international events such as conferences, campaigns, forums, and summits.

The Correspondence series contains both personal and organizational correspondence. Electronic mail and paper mail items are intermixed. Items of interest include letters from Bill Clinton, Hillary Clinton, and the Reverend Jesse Jackson. Campaign contributors’ correspondence from O’Brien’s 2006 bid for the Iowa Secretary of Agriculture can also be found in this series. Correspondence to and from Briana Harris is located in the Biographical and family series.

The Organizational Involvement series consists of records, papers, notes, and information from or about organizations in which O'Brien has been a member, officer, or observer. Her work with the WFAN (Women, Food, & Agriculture Network) as a founding member along with her fellowship role as a WK Kellogg Food and Society Policy Fellow are both highlighted in individual sub-series. The WFAN sub-series covers general information and resources from the organization while the WK Kellogg Food and Society Policy Fellow sub-series includes materials from her trip to the Costa Rican EARTH University and the numerous notebooks O’Brien filled while she was a WK Kellogg fellow.

The Resource Files series contains books, magazines, newspaper articles, pamphlets, and memos maintained by O'Brien for informational purposes. These files concern agricultural organizations, agribusiness and environmental issues, Bovine Growth Hormone (BGH) and Bovine somatotropin (BST), the farm crisis and farm bills, General Agreement on Tariffs and Trade (GATT), health care and insurance, North American Free Trade Agreement (NAFTA), sustainable agriculture, and women's organizations. Resources also include information about various ecofeminist causes such as international women in agriculture and newspaper clippings about Iowan female farmers.

The Writings series contains notebooks in which O'Brien recorded her thoughts and reactions during the many meetings and conferences that she attended, as well as professional writings and speeches. It also includes texts of testimony she presented at various public hearings and a copy of the speech she gave to the United Nations on behalf of the world’s farmers.

The Photographs series contains photographs of O'Brien, members of her family, friends, and the farmstead.

The Artifacts series consists of nametags, pins, and folders from numerous conferences, as well as bumper stickers. It also includes a plaque for the Dixon Terry Leadership Award she received in 1992 from the Iowa Farm Unity Coalition. The series concludes with campaign T-shirts and memorabilia such as a button from O’Brien’s 2006 bid for Iowa Secretary of Agriculture.