Defiance County is a county located in the U.S. state of Ohio. According to the 2010 census, it has a population of 39,037, which is a decrease of 1.2% from 39,500 in 2000. Its county seat is Defiance. The county was named after an early Army fortification, Fort Defiance, which was named that by Mad Anthony Wayne to signify the settler's "defiance" of the Indians.
The Defiance, OH Micropolitan Statistical Area includes all of Defiance County.