Secondary sources are materials written by historians using primary sources (such as government reports, newspaper articles, memoirs, etc.) Examples of secondary sources include books, journal articles, and encyclopedia articles. For the full secondary sources guide, see http://guides.ou.edu/history
For the history of the University of Oklahoma, see: http://guides.ou.edu/ouhistory.
To search for books on the history of Oklahoma, use Discover Local (the catalog). It lists materials owned by the University of Oklahoma Libraries.
Many cities and counties have written their histories. These can be good secondary resources, and occasionally these may serve as primary resources if they include first-hand accounts of life in a place. To locate county histories in Discover Local, search the words "county history Oklahoma" (without the quotes) in the "Any" category, limiting "Material Type" to "Books." Another good way to locate a county or town history is to search for that place in the subject category.
There are also a few general state histories and encyclopedias that are good secondary resources. Check the bibliographies and footnotes to find primary resources that fit your topic. See below for links to these resources.
There are several Oklahoma-related journals and magazines. Most of these resources may be found both in print and digital formats. See the links below for more detailed descriptions.
The database America: History and Life indexes journal articles and more. Click here for a search that includes the subject of Oklahoma. NOTE: The library has licensed this database for 6 simultaneous users.