It is thought that the area has been the site of human habitation since at least 2500 B.C. Dolores County's western portions were densely populated between 900 and 1300 AD. Population estimates of as many as 10,000 population, with villages of hundreds of rooms, have been made by archaeologists and other researchers. But this population was destroyed or migrated elsewhere, apparently following a drought and severe societal upheaval in the 14th century, and for centuries thereafter, both the western and eastern mountainous areas of the county were occupied mostly by nomads, including the Ute and the Navajo Indians. Like much of southwestern Colorado, Dolores County is rich in Indian ruins and sites of the Anasazi. According to the Anasazi Heritage Center, Dolores County contains at least 816 recorded archaeological sites as of 1989, with many more inventoried since that time.
The county also contains a portion of a site of regional historic interest, the Dominguez-Escalante Trail of 1776. The trail marks a historic 1,800-mile (2,900 km) trip, intended to discover an overland route between Santa Fe, New Mexico and Monterey, California. The Expedition camped on Dove Creek in the western portion of the county. The Old Spanish Trail later passed through the western portion of the County.
Anglo trappers worked the mountains of eastern Dolores County as early as 1832-33, and gold was discovered in the County in 1866. But it was not until the area was taken from the Ute and removed from the Ute Reservation by the Brunot Agreement of 1878 that large-scale minerals exploration and mining began in the county, although the Pioneer Mining District was established (illegally) in 1876 in the Rico area. The development of the area was spurred by the discovery of large silver deposits near Rico in 1879, and the Rio Grande Southern Railroad was constructed through the County to connect Durango, Telluride, and Ridgway in 1890-92 The RGS served the eastern end of Dolores County until 1952 when it was abandoned. (The western portion of the county has never had railroad service.)
Rico's high point was in 1892, when the mining district population was more than 5,000; three times the current population of the entire county. The 1893 Silver Panic hit the town hard; by 1900 the population was 811. The mountainous area of Dolores County went through a series of booms and busts through the 20th Century. The low point of the community came in 1974 with an estimated population of 45; since then the town has become a bedroom community for Telluride and has limited tourism and subdivisions; the population has rebounded to almost 300. Efforts are underway in the early 21st Century to again begin major mining activities in the region.
Dove Creek was a way station on the Old Spanish Trail from the mid 19th century, for caravans and travelers moving between Santa Fe, Salt Lake City, and northern California and Nevada. The western portion of the county was used, beginning in the 1870s, for cattle ranching, but the lush grass soon suffered from overgrazing and then fire suppression, allowing the massive expansion of sagebrush, pinyon, and juniper. Homesteading in the area became common beginning in 1914, and dryland farming expanded throughout the Great Sage Plain. Today dryland farming of pinto beans and winter wheat is still a mainstay of the county's economy. But the development of irrigation using water from the Dolores Project in the 1980s, with the construction of McPhee Reservoir (immediately upstream in Montezuma County), has changed the history and population of the county.