San Juan County is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 705, making it the least populous county in Colorado. The county seat and the only incorporated municipality in the county is Silverton. The county name is the Spanish language name for "Saint John", the name Spanish explorers gave to a river and the mountain range in the area. With a mean elevation of 11,240 feet, San Juan County is the highest county in the United States and also has the two highest elevation houses in the United States; the ‘Bonnie Belle’ above Animas Forks at 11,900’ – 11,950’ elevation and an unnamed house above Picayune Gulch at 12,000’ elevation.

The San Juan Mountains is a high and rugged mountain range in the Rocky Mountains in southwestern Colorado and northwestern New Mexico. The area is highly mineralized and figured in the gold and silver mining industry of early Colorado. Major towns, all old mining camps, include Creede, Lake City, Silverton, Ouray, and Telluride. Large scale mining has ended in the region, although independent prospectors still work claims throughout the range. The last large-scale mines were the Sunnyside Mine near Silverton, which operated until late in the 20th century, and the Idarado Mine on Red Mountain Pass, which closed in the 1970s. Famous old San Juan mines include the Camp Bird and Smuggler Union mines, both located between Telluride and Ouray.