Cass County is a county located in the western part of the U.S. state of Missouri and is part of the Kansas City metropolitan area. As of the 2020 census, the population was 107,824. Its county seat is Harrisonville; however, the county contains a portion of Kansas City, Missouri. The county was organized in 1835 as Van Buren County, but was renamed in 1849 after U.S. Senator Lewis Cass of Michigan, who later became a presidential candidate.

The Kansas City metropolitan area is a bi-state metropolitan area anchored by Kansas City, Missouri. Its 14 counties straddle the border between the U.S. states of Missouri and Kansas. With 8,472 square miles (21,940 km2) and a population of more than 2.2 million people, it is the second-largest metropolitan area centered in Missouri and is the largest metropolitan area in Kansas, though Wichita is the largest metropolitan area centered in Kansas. Alongside Kansas City, Missouri, these are the suburbs with populations above 100,000: Overland Park, Kansas; Kansas City, Kansas; Olathe, Kansas; Independence, Missouri; and Lee's Summit, Missouri.