Cochise County is a county in the southeastern corner of the U.S. state of Arizona. It is named after Cochise, a Chiricahua Apache who was a key war leader during the Apache Wars. The population was 125,447 at the 2020 census. The county seat is Bisbee and the most populous city is Sierra Vista. Cochise County includes the Sierra Vista-Douglas, Arizona Metropolitan Statistical Area. The county borders southwestern New Mexico and the northwestern Mexican state of Sonora.