Clark, Horace Spencer was born on August 12, 1840 in Huntsburg, Ohio, United States. Son of Joseph M. P. and Charlotte (Brainerd) Clark.
Educated in Ohio public schools, Iowa State University: m. Harriet E. Betts, May 3, 1864. First lieutenant Company E, 73d Ohio volunteer infantry, discharged on account of wounds at Gettysburg, July 3, 1863.
Judge of Mattoon City Court. State senator Illinois, 1880-1884. Delegate at large Republican National Convention, 1888.
Commander G.A.R., department of Illinois, 1891. Republican elector at large, 1896, and chairman Electoral College, Illinois. Brigadier general commanding 2d brigade Illinois National Guard.