This collection contains general correspondence of members of the Sidney Edgerton family including letters (1859-1884) written while crossing the plains, and later while living in Bannack, Montana Territory. Subgroups of correspondents include Sidney Edgerton, Mary Wright Edgerton, Martha "Mattie" Edgerton Rolfe, (Mary) Pauline Edgerton, Wright Prescott Edgerton, and Lucia Aurora Darling. Also included in Sidney Edgerton's papers is biographical material in the form of clippings maintained originally as a scrapbook; legal documents, including his official appointment as territorial governor; a treaty with the Flatheads signed by Chief Victor; and a speech concerning slavery. The collection generally provides information on frontier and pioneer life, crossing the plains by covered wagon, local color in Bannack (including information on road-agents and vigilantes), and the infancy of political organization in Montana.