There are 4 US Post Offices in Adair County serving a total of 25,472 residents equating to 6,368 residents per post office. It's estimated that approximately 40,656 packages are handled across the 4 county post offices annually. Adair County is a county located in the northeastern part of the U.S. state of Missouri. As of the 2010 Census, the population was 25,607. Its county seat is Kirksville. The county was organized January 29, 1841 and named for Governor John Adair of Kentucky. Adair County comprises the Kirksville, MO Micropolitan Statistical Area.