The Society of Montana Pioneers was founded on September 11, 1884 in Helena, Montana, to honor and document the histories of Montana pioneers who were resident in the territory at the time it became a Montana Territory, May 26, 1864. In 1909, the society changed its membership rules to admit pioneers who were resident the territory prior to December 31, 1868. In 1899, the society boasted 1536 active members out of a one time total of 1808. The society did not consider individuals who were assigned to Montana on military duties, individuals who were deemed outlaws such as Henry Plummer of Bannack, or Indians as eligible for membership in the society.