There are 6 US Post Offices in Pettis County serving a total of 41,334 residents equating to 6,889 residents per post office. It's estimated that approximately 65,974 packages are handled across the 6 county post offices annually. Pettis County is a county county located in the western county portion of the county U.S. state of Missouri. As of the 2010 census, the population was 42,201. Its county seat is Sedalia. The county was organized January 24, 1833, and named after former U.S. Representative Spencer Darwin Pettis. Pettis County comprises the Sedalia, MO Micropolitan Statistical Area. The county is home to the site of the Missouri State Fair in Sedalia."