The papers of William Allen (1803-1879) span the years 1796-1879, with the bulk of the items concentrated in the period 1840-1876. The collection focuses on his career in Ohio politics, first as United States representative and senator, then as governor of Ohio. Included are correspondence, speeches, memoranda, financial records, printed matter, maps, and other material. The papers are arranged in a bound Chronological File and a Miscellany.

The Chronological File consists primarily of correspondence, financial records, maps, and other material concerning Ohio and national politics during the 1840s and the 1870s. Topics include support of the United States annexation of Texas, the Mexican War, Oregon claims, land surveys, and the Greenback movement. Correspondents include James Faran, James Graham, John Hough, Amos Layman, George Morgan, and Henry A. Whitman.

The Miscellany consists of an account book of the Stoney Mill Salt Works, Chillicothe, Ohio, dating from 1811 to 1823, which Allen used partially as the backing for a scrapbook of clippings from 1825 to 1827. Also in the series are cancelled bank checks, an 1838 directory of the United States government, memoranda books containing jottings and accounting notes, newspaper clippings, a notebook, a promissory note, political literature, a scrapbook, speeches by Allen and others, and the records of the Chillicothe Independent Blues, an Ohio militia corps.