Fort Defiance (Navajo: Tséhootsooí [tsʰéhòːtsʰòː.í]) is a census-designated place (CDP) in Apache County, Arizona, United States.

[3] The land on which Fort Defiance was eventually established was first noted by the U.S. military when Colonel John Washington stopped there on his return journey from an expedition to Canyon de Chelly.

[5] Fort Defiance was established on September 18, 1851, by Col. Edwin V. Sumner to create a military presence in Diné bikéyah (Navajo territory).

Sumner broke up the fort at Santa Fe for this purpose, creating the first military post in what is now Arizona.

[5] Fort Defiance was built on valuable grazing land that the federal government then prohibited the Navajo from using.

Continued Navajo raids in the area led Brigadier General James H. Carleton to send Kit Carson to impose order.

General Carleton's "solution" was brutal: thousands of starving Navajo were forced on a Long Walk of 450 miles (720 km) and interned near Fort Sumner, New Mexico, and much of their livestock was destroyed.

The Navajo Treaty of 1868 allowed those interned to return to a portion of their land, and Fort Defiance was reestablished as an Indian agency that year.