There are 7 US Post Offices in Knox County serving a total of 4,144 residents equating to 592 residents per post office. It's estimated that approximately 6,614 packages are handled across the 7 county post offices annually. Knox County is a county located in the northeast portion of the U.S. state of Missouri. As of the 2010 census, the population was 4,131, making it the third-least populous county in Missouri. Its county seat is Edina. The county was organized February 14, 1845 and named for U.S. Secretary of War General Henry Knox."