Cooper County is located in the central portion of the U.S. state of Missouri. As of the 2020 United States census, the population was 17,103. Its county seat is Boonville. The county was organized December 17, 1818, and named for Sarshell Cooper, a frontier settler who was killed by Native Americans near Arrow Rock in 1814. It is a part of the Columbia, Missouri metropolitan area.

Moniteau County is a county located in the U.S. state of Missouri. As of the 2020 United States census, the population was 15,473. Its county seat is California. The county was organized February 14, 1845, and named for the Moniteau Creek. 'Moniteau' is a French spelling of Manitou, Algonquian for the Great Spirit.