Blaine County is a county in the U.S. state of Idaho. As of the 2020 United States Census, the population was 24,272. The county seat and largest city is Hailey. It is also home to the Sun Valley ski resort, adjacent to Ketchum. Blaine County was created by the territorial legislature on March 5, 1895, by combining Alturas and Logan counties; it was named for former congressman and 1884 Republican presidential nominee James G. Blaine.