Adair County is a county located in the U.S. state of Oklahoma. As of the 2020 census, the population was 19,495. Its county seat is Stilwell. Adair County was named after the Adair family of the Cherokee tribe. One source says that the county was specifically named for Watt Adair, one of the first Cherokees to settle in the area. Adair County is part of the Cherokee Nation reservation.