To browse books on Oklahoma history, go to the 4th floor of Dulaney-Browne Library, call number 976.6
Besides WorldCat Discovery (below), try searching HathiTrust to find digitized books and other documents on Oklahoma history (19th century-early 20th century):
Here are some sample subject headings and their search results in WorldCat Discovery:
In WorldCat Discovery, you enter a search term, and then limit your search using filters on the left-hand side of display.
For example, the results below are limited to print books that Oklahoma City University has access to. You can also limit your results to articles or ebooks: