Coconino County is a county in the North-Central part of the U.S. state of Arizona. Its population was 145,101 at the 2020 census. The county seat is Flagstaff. The county takes its name from Cohonino, a name applied to the Havasupai people. It is the second-largest county by area in the contiguous United States, behind San Bernardino County, California. It has 18,661 sq mi (48,332 km²), or 16.4% of Arizona's total area, and is larger than the nine smallest states in the U.S.