Jefferson County administrative offices are located at 100 Jefferson County Parkway, Golden, CO 80419; phone: 303‑279‑6511.
Situated in the north-central part of Colorado, Jefferson County is one of the original 17 territorial counties. Its location along the Front Range made it a gateway to the mountains for indigenous peoples and for Euro-American gold seekers who arrived in this remote western territory beginning in late 1858. Prospectors had discovered a small amount of gold in 1850 at Ralston Creek in present-day Jefferson County. During the gold rush of the late 1850s and early 1860s, some placer mining occurred in Clear Creek east of present-day Golden, but little gold was discovered in what would become Jefferson County. Instead, the county prospered by providing transportation, food, timber, coal, bricks, and supplies to Denver and to mining districts in Gilpin and Clear Creek counties. Abundant natural resources contributed to this early growth—fertile farmland, vast timber stands, and deposits of stone, clay, and coal supported early industries. In the twentieth century, the county's scenic beauty and the availability of the automobile encouraged tourism and outdoor recreation as important industries in the western mountains. Development of the Denver Mountain Parks and the Pike, Arapahoe, and Roosevelt National Forests encouraged outdoor activity and stimulated construction of summer dwellings in western Jefferson County, ranging from small wood-frame cottages to elaborate stone lodges.