The trappers and traders of the early 19th century left little behind them except endangered species. There were no roads, no communications networks, and almost no settlements (from this era, only Fort Benton still exists as a community).

James and Granville Stuart discovered gold on Gold Creek near Deer Lodge in 1860. In 1862 gold was found on Grasshopper Creek near Bannack, and the next year saw prospecting along Alder Gulch near Virginia City. Last Chance Gulch, which was to become Helena, boomed in 1864.

These large strikes and many smaller mines attracted people of varied character to Montana. Fewer than 100 whites were in the state in 1860. By 1870 there were more than 20,000. Some men came to Montana to prospect for gold and get rich; others came to get rich by stealing and killing. Travel between the settlements of Virginia City, Bannack, and other mining camps became increasingly dangerous as “road agents” preyed on stagecoaches and miners.

For its protection, Virginia City elected Henry Plummer as sheriff. Plummer, however, doubled as leader of the principal gang of road agents, called the “Innocents.” More than 100 people were killed by the Innocents during 1862–1863. In response, committees of vigilantes formed, which reached summary judgment and hanged the Innocents.

By 1870, approximately $100 million in gold had been extracted from Montana claims. The advent of great wealth and private property soon made firm government and community lawfulness imperative. In 1864, Montana became a territory, with Bannack its capital. Schools, churches, and other civic institutions were established in Virginia City. Miners began bringing their families out to the frontier to settle.