In the Wild West, law was often non-existent. Many times vigilantes took enforcement of the law, as well as moral codes, into their own hands. Vigilantes were most common in mining communities, but were also known to exist in cow towns and farming settlements. Mostly these groups formed before any law and order existed in a new settlement. Justice, including whipping and banishment, but mostly the offenders were lynched.
Many times the vigilantes were seen as heroes and supported by law abiding citizens, seen as a much needed step to fill a gap. There were literally hundreds of vigilante groups that formed in the old American West.
Following the Civil War, the Reno Gang began to terrorize the Midwest. This resulted in the formation of the Southern Indiana Vigilance Committee. The next time the Reno Gang attempted to rob a train, the vigilante group lynched its leaders, Frank, William, and Simon Reno.
During Montana's gold rush days of 1863, the law was sometimes non-existent in the region that was then the Territory of Idaho. However in Virginia City there was a law of sorts. When a young miner was found murdered, a posse was quickly formed to track down the killers. They soon returned with three suspects who were tried in December 1863. One man was convicted and hanged for the crime, but of the other two, one was banished from the territory and the other set free. Outraged locals decided that justice in the court was slow and ineffective, and the Montana Vigilantes was born. Five members were originally sworn in as the Montana Vigilance Committee, and almost immediately orderly arrests and trial courts became obsolete, as a reign of lynchings began. By the end of February 1864, 22 men had been lynched. Today historians disagree as to whether the men that were hanged during the Montana Vigilante days were truly guilty. As a warning to other criminals in Montana, vigilantes began leaving a slip of paper on the hanged corpses with the cryptic numbers "3-7-77". Although the meaning is unclear, many claim it referred to the dimensions of a grave; 3 feet wide, 7 feet long, and 77 inches deep. Random lynchings continued in Montana throughout the 1860s until a backlash against extralegal justice finally took hold around 1870.
Probably the most famous of modern day vigilantes are Bernhard Goetz (the Subway Vigilante), and Jack Ruby, the self appointed vigilante who shot and killed Lee Harvey Oswald, the alleged killer of President Kennedy.