The county was officially established in 1808. Portions of the county were later separated into parts of Crawford, Floyd, Washington, Jackson, Clark, Lawrence, Perry, Scott, and Orange Counties. The county was later named for William Henry Harrison, the first governor of Indiana Territory, a General in War of 1812, a hero of Tippecanoe, and the 9th U.S. President. The county has a total area of 486 square miles with a population count of 40,354 residents.