James Michael Cavanaugh was a U.S. Representative from Minnesota and a delegate from the Territory of Montana. He was born in Springfield, Massachusetts, July 4, 1823 and received an academic education. He engaged in newspaper work, studied law, and was admitted to the bar in 1854 and began practice in Davenport, Iowa. He then moved to Chatfield, Fillmore County, Minnesota, in 1854 and continued the practice of law; upon the admission of Minnesota as a State into the Union, in 1858, was elected as a Democrat to the thirty-fifth congress and served from May 11, 1858, to March 3, 1859; unsuccessful candidate for re-election in 1858 to the thirty-sixth congress; moved to Colorado in 1861 and resumed the practice of law; also engaged in mining; member of the State constitutional convention in 1865; moved to Montana in 1866; as a Democrat, he was elected a delegate to the fortieth and forty-first congresses ; unsuccessful candidate for renomination in 1870; engaged in the practice of law in New York City; returned to Colorado in 1879 and settled in Leadville, where he died October 30, 1879. He is buried in the Greenwood Cemetery in New York City.

The Territory of Montana was an organized incorporated territory of the United States that existed from May 26, 1864, until November 8, 1889, when it was admitted as the 41st state in the Union as the state of Montana.