Henry Plummer was born in Houlton, Maine, in 1832. Ed and Rial Plummer and their eight children moved to Sauk County, Wisconsin in 1845.
Plummer did a variety of jobs before becoming a part owner of a bakery. In 1855 Plummer was appointed deputy sheriff to David Johnson of Nevada City. The following year he was elected to replace Johnson as marshal. This result was disputed by Johnson but he was killed in dubious circumstances on 3rd November, 1856. It was not clear what role Plummer played in this but there was no doubt about his killing of John Vedder on 26th September, 1857. Plummer, who had been having an affair with Vedder's wife, was sentenced to 10 years in San Quentin.
Plummer convinced the prison authorities that he was suffering from tuberculosis and in August, 1859, he was released on health grounds. He returned to Nevada City and on 13th February, 1861, Plummer badly wounded W. J. Muldoon in a dispute that took place in a brothel. Muldoon later died of his injuries. Later that year Plummer killed William Riley in a fight.
Plummer's friend, Billy Mayfield, killed Sheriff John Blackburn of Carson City. The two men fled and for a while lived at Walla Walla. Later they moved to Idaho where they formed a gang that robbed and terrorized families living and working in local mining camps. After a Vigilante Committee was formed, Plummer moved to Montana. Soon afterwards Jack Cleveland was killed by Plummer. It is believed that the reason for the killing was that Cleveland was threatening to expose Plummer's past.
In May 1863, Plummer was elected sheriff of Bannack . Unknown to the people of Bannack, Plummer was the leader a 100 man gang that were involved in local robberies. The gang wore ties in a special knot to identify fellow members and called themselves as the "Innocents". Crime in the town increased dramatically and in during the first couple of months after he was appointed, more than 100 citizens were murdered. A Vigilante Committee was formed and eventually a member of the Innocents confessed that Plummer was the gang's leader. On 10th January, 1864, Henry Plummer was lynched by the vigilantes.