Fort Defiance is a census-designated place (CDP) in Apache County, Arizona, United States. It is also located within the Navajo Nation. The population was 3,624 at the 2010 census.

Navajo or Navaho is a Southern Athabaskan language of the Na-Dené family, through which it is related to languages spoken across the western areas of North America. Navajo is spoken primarily in the Southwestern United States, especially in the Navajo Nation. It is one of the most widely spoken Native American languages and is the most widely spoken north of the Mexico–United States border, with almost 170,000 Americans speaking Navajo at home as of 2011.