迪法恩斯县（Defiance County, Ohio）是美国俄亥俄州西北部的一个县，西邻伊利诺伊州。面积1,073平方公里。根据美国2000年人口普查，共有人口39,500人。县治迪法恩斯 (Defiance)。

成立于1820年2月12日，县名来自筑以防卫印地安人的迪法恩斯堡 (Fort Defiance)，指的是印地安人的挑战。

Defiance County is a county located in the U.S. state of Ohio. As of the 2010 census, the population was 39,037. Its county seat is Defiance. The county was named after an early Army fortification, Fort Defiance, which was so named by Mad Anthony Wayne to signify the settlers' "defiance" of the Indians.