The first known explorer of Diamond Valley was Colonel John C. Fremont, who mapped the area to aid western migration in 1845. Before Fremont, tribes of Shoshone and Paiute Indians long had gathered nature's bounty here.

Colonel J.H. Simpson mapped a route through the valley in 1859. The Simpson route, through the north end of the valley, immediately became the Pony Express route from 1860-1861. The Overland telegraph replaced the Pony Express and also crossed the valley.

Early freight toll roads were operated across the valley as lead and silver mining camps boomed in the 1860's. Needs of the mining camps gave rise to a limited livestock and dairy industry. In 1957, a large underground lake was tapped to supply water for irrigation.