Sidney Edgerton was an American politician, lawyer, judge and teacher from Ohio. He served during the American Civil War, as a Squirrel Hunter. During this time, Edgerton served as a U.S. Congressman. In 1863, Abraham Lincoln appointed him the first Chief justice of the Idaho Territorial Supreme Court. Edgerton lobbied for the creation of separate territories, out of the Idaho Territory, and in 1864, Abraham Lincoln appointed Edgerton as the first Territorial Governor of Montana. During his term as Territorial Governor, he was an alleged member of the infamous Montana Vigilantes, and was reputedly among its founders.

The history of vigilante justice and the Montana Vigilantes began in 1863 in what was at the time a remote part of eastern Idaho Territory. Vigilante activities continued, although somewhat sporadically, through the Montana Territorial period until the territory became the state of Montana on November 8, 1889. Vigilantism arose because territorial law enforcement and the courts had very little power in the remote mining camps during the territorial period.