Established September 1, 1851, but having remained without organization till 1897, this county commemorates the distinguished statesman Lewis Cass, who in 1820 commanded an exploring expedition that started from Detroit, passed through Lakes Huron and Superior, and thence advanced by way of Sandy Lake and the upper Mississippi as far as to the upper Red Cedar Lake. This name, a translation from the Ojibwe name, was changed by Henry R. Schoolcraft, the narrator of the expedition, to be Cassina or Cass Lake, in honor of its commander. He was born in Exeter, N.H., October 9, 1782, and died in Detroit, Mich., June 17, 1866. At the age of 18 years he came to Marietta, the first town founded in southern Ohio, and studied law there; was admitted to the bar in 1803 and began practice at Zanesville, Ohio; and was colonel and later brigadier general in the War of 1812. He was governor of Michigan Territory, 1813 to 1831; negotiated 22 treaties with Indian tribes; was secretary of war in the cabinet of President Andrew Jackson, 1831-36, including the time of the Black Hawk War; was minister to France, 1836-42; U.S. senator, 1845-48; Democratic candidate for the presidency in the campaign of 1848; again U.S. senator, 1849-57; and secretary of state in the cabinet of President James Buchanan, 1857-60.

To voyage along the upper Mississippi River and to describe and map its principal source were the motives for the expedition undertaken in 1820 by Cass. At this time Michigan Territory, of which he was governor, included the northeastern third of Minnesota, east of the Mississippi, and Missouri Territory extended across the present state of Iowa and western two-thirds of Minnesota.

The report of this expedition, published the next year, is titled Narrative Journal of Travels from Detroit Northwest through the Great Chain of American Lakes to the Sources of the Mississippi River in the Year 1820, by Henry R. Schoolcraft . . . 1821 (424 pp., with a map and eight copper-plate engravings). This title page is engraved and is followed by another in print, which states that the author was "a member of the Expedition under Governor Cass." The explorations of the upper Mississippi by Cass and Schoolcraft, of whom the latter visited and named Lake Itasca in 1832, are related in a chapter of Minnesota in Three Centuries (1908, vol. I, pp. 347-56, with their portraits).

Several extended biographies of Gen. Cass were published during his lifetime, in 1848, 1852, and 1856, the years of successive presidential campaigns. In 1889 a marble statue of him was contributed by the state of Michigan as one of its two statues for the National Statuary Hall at the Capitol in Washington, and the proceedings and addresses in Congress upon the acceptance of the statue were published in a volume of 106 pages. Two years afterward, in 1891, a mature study of his biography, titled Lewis Cass, by Andrew C. McLaughlin, Assistant Professor of History in the University of Michigan (363 pp.), was published in the "American Statesmen" series.