The bulk of this series concerns Samuel R. Thurston's political career as a delegate in U.S. Congress, and includes correspondence from constituents in the Oregon Territory.

Frequent topics of discussion in correspondence are the Oregon Donation Land Law; current events in the Oregon Territory; the legal status of John McLoughlin's claim in Oregon City, and of lots sold from McLoughlin's claim to Euro-American emigrants; and the Oregon Statesman and Oregon Spectator newspapers. Other notable correspondence includes a letter from Peter H. Burnett, relating his role in the formation of the California state government; letters from William P. Bryant concerning his resignation as chief justice of the Oregon Supreme Court; and a letter from Henry H. Spalding about his position as postmaster and the execution of five Cayuse men for the Whitman killings.

Thurston's political activities are also represented through his speeches to Congress, most of which concern the Oregon Territory and the Oregon Donation Land Law. These speeches include derogatory language and sentiments towards John McLoughlin, Indigenous peoples, and Black Americans.

Other papers in this series include personal correspondence, particularly Thurston's letters to his wife, Elizabeth; transcribed diary entries detailing his travel to and work in Washington, D.C.; Thurston's notes and writings; receipts and promissory notes; agreements; a commission as a notary public in Maine; and documents relating to his death.