El Dorado County was one of the original counties of California, created in 1850 at the time of statehood. Parts of the county's territory were given to Amador County in 1854 and to Alpine County in 1864. Prior to statehood, it had been referred to as Coloma County.

The county derives its name from "El Dorado" -- the far-famed fabulous region of genial clime and never-fading verdure, where gold and precious stones are as common as rocks and pebbles, where wines gently flow from fountains. The name, meaning "the gilded one" in Spanish, appears at the beginning of the 16th century as that of a mythical Native American chief who was said to have been covered with gold dust during the performance of religious rites. When the discovery of gold by James W. Marshall at Coloma in January 1848 became known to the world, California, and particularly that section where gold was discovered, was called "El Dorado."