Harrisonville is a city in Cass County, Missouri, United States. The population was 8,946 at the 2000 census. It is the county seat of Cass County. Harrisonville was found in 1837, and was named for Congressman Albert G. Harrison. The area suffered greatly during the American Civil War, though Harrisonville was one of the few places exempted in Union General Thomas Ewing's notorious General Order No. 11 (1863), which ordered the depopulation of four entire Missouri counties.