There are 3 US Post Offices in Adair County serving a total of 16,272 residents equating to 5,424 residents per post office. It's estimated that approximately 25,972 packages are handled across the 3 county post offices annually. Adair County is a county located in the U.S. state of Kentucky. As of the 2010 census, the population was 18,656. Its county seat is Columbia. The county was founded in 1801 and named for John Adair, then Speaker of the House in Kentucky and later Governor of Kentucky (1820 - 1824). Adair County has one of the few surviving American Chestnut trees in the United States. Adair County is a wet county as of March 23, 2016.