Harrisonville is a city in Cass County, Missouri, United States. The population was 10,019 at the 2010 census. It is the county seat of Cass County. Harrisonville was founded in 1837 upon land donated to Cass County by Congress for county purposes, and was named for Congressman Albert G. Harrison, who was instrumental in obtaining the land grant. 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 three entire Missouri counties and part of a fourth.