There are 6 US Post Offices in Shelby County serving a total of 6,152 residents equating to 1,025 residents per post office. It's estimated that approximately 9,819 packages are handled across the 6 county post offices annually. Shelby County is a county located in the northeastern portion of the U.S. state of Missouri. As of the 2010 census, the population was 6,373. Its county seat is Shelbyville. The county was organized January 2, 1835 and named for Governor Isaac Shelby of Kentucky.