Adair County is a county located in the northeastern part of the U.S. state of Missouri. The population census for 2020 was 25,314. As of July 1, 2021, the U.S. Census Bureau's Population Estimates for the county is 25,185, a -0.5% change. Adair county seat is Kirksville. The county was first settled by immigrants from Kentucky and organized on January 29, 1841. Adair County comprises the Kirksville, MO Micropolitan Statistical Area.

Kirksville is the county seat and most populous city in Adair County, Missouri. Located in Benton Township, its population was 17,530 at the 2020 census. Kirksville is home to three colleges: Truman State University, Moberly Area Community College, and A.T. Still University.