Jackson County is located in the western portion of the U.S. state of Missouri, on the border with Kansas. As of the 2020 census, the population was 717,204. making it the second-most populous county in the state. Although Independence retains its status as the original county seat, Kansas City, Missouri, serves as a second county seat and the cente…Jackson County is located in the western portion of the U.S. state of Missouri, on the border with Kansas. As of the 2020 census, the population was 717,204. making it the second-most populous county in the state. Although Independence retains its status as the original county seat, Kansas City, Missouri, serves as a second county seat and the center of county government. The county was organized December 15, 1826, and named for former Tennessee senator Andrew Jackson, who would become President of the United States three years later in 1829.