There are 7 US Post Offices in Cooper County serving a total of 17,405 residents equating to 2,486 residents per post office. It's estimated that approximately 27,780 packages are handled across the 7 county post offices annually. Cooper County is a county located in the central portion of the U.S. state of Missouri. As of the 2010 census, the population was 17,601. 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.