Iron County is a county located in the Lead Belt region in the U.S. state of Missouri. As of the 2020 census, the population was 9,537. The largest city and county seat is Ironton. Iron County was officially organized on February 17, 1857, and was named after the abundance of iron ore found within its borders. Iron County includes the 6-mile-long, 2-mile-wide Arcadia Valley, the site of Pilot Knob, Ironton, and Arcadia, communities established by immigrants in the 19th Century.