The Fort Irwin area has a history dating back almost 15,000 years, when Native Americans of the Lake Mojave Period were believed to live in the area. Native American settlements and pioneer explorations in the area were first recorded when Father Francisco Garces, a Spaniard, traveled the Mojave Indian Trail in 1796. During his travels, he noted several small bands of Indians and is believed to have been the first European to make contact with the Native Americans of this area.
Jedediah Smith is thought to have been the first American to explore the area in 1826. A fur trapper, Smith was soon followed by other pioneers traveling the Old Spanish Trail between Santa Fe and Los Angeles. Bitter Springs, on the eastern edge of Fort Irwin, was a favorite stop over site.
In 1844, Captain John C. Fremont, accompanied by Kit Carson, was the first member of the US Army to visit the Fort Irwin area. Captain Fremont established a camp near Bitter Springs that served travelers on the Old Spanish Trail, and later the Mormon Trail, linking Salt Lake City to California. This camp was later to become an important supply center for pioneers during California's settlement and gold rush.
The California Gold Rush brought prosperous trade and unexpected trouble to the area. As California grew, and more travelers used the trails to enter the territory, raids and horse stealing became a problem. In 1846, the Army's Mormon Battalion patrolled the Fort Irwin area to control the raiding and horse stealing. During the Indian Wars the Army constructed a small stone fort overlooking Bitter Springs and patrolled the Fort Irwin area.
The years following the Indian Wars were quiet militarily. In 1940, President Franklin D. Roosevelt established the Mojave Anti-Aircraft Range, a military reservation of approximately 1,000 square miles (3,000 km2) in the area of the present Fort Irwin. In 1942, the Mojave Anti-Aircraft Range was renamed Camp Irwin, in honor of Major General George LeRoy Irwin, commander of the 57th Field Artillery Brigade during World War I, and it was subsumed into the Desert Training Center as one of its cantonment areas and some of its ranges. Two years later, Camp Irwin was deactivated and placed on surplus status.
Camp Irwin reopened its gates in 1951 as the Armored Combat Training Area and served as a training center for combat units during the Korean War. Regimental tank companies of the U.S. 43d Infantry Division from Camp Pickett, Virginia were the first to train at the new facility.
The post was designated a permanent installation on 1 August 1961 and renamed Fort Irwin. During the Vietnam buildup, many units, primarily artillery and engineer, trained and deployed from Fort Irwin.
In January 1971, the post was deactivated again and placed in maintenance status under the control of Fort MacArthur (Los Angeles), California. The California National Guard assumed full responsibility for the post in 1972. From 1972 to late 1980, Fort Irwin was used primarily as a training area by the National Guard and reserve components.
On 9 August 1979, the Department of the Army announced that Fort Irwin had been selected as the site for the National Training Center. With over 1,000 square miles (2,600 km2) for maneuver and ranges, an uncluttered electromagnetic spectrum, airspace restricted to military use, and its isolation from densely populated areas, Fort Irwin was an ideal site for this facility. The National Training Center was officially activated 16 October 1980, and Fort Irwin returned to active status on 1 July 1981.
The National Training Center and Fort Irwin continues to serve as the Army's premier training center. After the September 11, 2001 attacks, the National Training Center transformed to focus on continuous counterinsurgency operations that reflected an ongoing and rapidly changing battlefield.