From the Encyclopedia of Mormonism:
Author: Flammer, Philip M.
The Illinois legislative act of December 1840 that incorporated the city of Nauvoo also authorized creation of a military body or militia that came to be known as the Nauvoo Legion. Perhaps influenced by genuine disgust with the way the Latter-day Saints had been treated in Missouri, the Illinois legislature acted liberally. Under the Nauvoo charter, Latter-day Saints could manage their own affairs, provided they did not violate the state or federal constitutions.
The organization of a militia unit was customary in settlements with sufficient population, a practice as old as the Republic. Nauvoo residents were particularly anxious to have their own military protection after having been victims of mob violence and having suffered expulsion from Missouri (see “Haun’s Mill Massacre.” By 1840, they realized that they could not always rely on federal or state authorities for protection from such violence.
The Nauvoo Court Martial, consisting of the legion’s commissioned officers, was given extensive authority. Among other things, it could “make, ordain, establish, and execute all such laws and ordinances as may be considered necessary for the benefit, government, and regulation of said Legion; provided [that] said Court Martial shall pass no law or act, repugnant to, or inconsistent with, the Constitution of the United States, or of this State [Illinois]” (HC 4:244).
As part of the state militia, the Nauvoo Legion was at the disposal of the governor of Illinois “for the public defense, and the execution of the laws of the State or of the United States.” Significantly, it was also at the disposal of the mayor of Nauvoo for “executing the laws and ordinances of the city corporation” (HC 4:244).
The city council ordinance that created the Nauvoo Legion authorized the rank of lieutenant general for its commanding officer, an extraordinary authorization, since no other militia officer in the United States held rank above that of major general. The court martial elected Joseph Smith, commander of the legion.
The parades and other activities of the legion-which included mock battles-attracted visitors from near and far. Indeed, the legion became so popular that many non-Mormons joined the ranks. At its peak, it is said to have numbered 5,000 men, the largest such body in Illinois. But there were problems. According to historian B. H. Roberts: [The Nauvoo Legion] excited the jealousy and envy of the rest of the militia in surrounding counties, and all the laudable efforts of the legion to become an efficient body with a view of assisting in the execution of the state and national laws, if occasion should require, were construed by their enemies to mean a preparation for rebellion…. Hence that which was to be a bulwark to the city, and a protection to the saints, was transformed by their enemies into an occasion of offense, and an excuse for distrusting them [CHC 2:59-60].
Joseph Smith mobilized the Nauvoo Legion to defend the city and declared martial law in June 1844 as tensions mounted between the Latter-day Saints, dissenters, and hostile neighbors. Joseph Smith and his brother Hyrum were among those arrested by another Illinois militia and placed in Carthage Jail, where they were killed by members of yet another militia (see “Martyrdom of Joseph and Hyrum Smith.” Six months later, the Illinois legislature revoked the Nauvoo Charter. At that point, the Nauvoo Legion ceased to exist as a state militia, although as an unofficial body it continued to provide some protection to the beleaguered Latter-day Saints.
During the exodus westward later, some former members of the Nauvoo Legion served in the Mormon Battalion. This 500-man body, authorized by the U.S. government in 1846 as part of the campaign against Mexico, marched from Council Bluffs to San Diego.
The name Nauvoo Legion was revived in Utah and applied to the organized militia of the state of Deseret and later of Utah Territory. This legion was called upon in 1849 to subdue marauding Indians, and its members served in the so-called Walker War of 1853-1854, named after Wakara, a Ute chieftain. With the approach of the Utah expedition in 1857-1858, the Utah militia harassed and burned U.S. Army supply trains and prepared, if necessary, to prevent the entry of U.S. troops into Salt Lake City. In 1862, during the American Civil War, two units of the Nauvoo Legion protected overland mail and telegraph lines. Later, with a force of some 2,500 men, it fought against Indians in Utah’s Black Hawk War (1865-1868).
Always more responsive to Mormon leadership than to the federal appointees who succeeded Brigham Young as governor of Utah, the legion was rendered inactive by an 1870 proclamation of Acting Governor J. Wilson Shaffer, who forbade gatherings of the militia except on his express orders. The Nauvoo Legion was finally disbanded as a result of the Edmunds-Tucker Act of 1887. In 1894 the National Guard of Utah was organized as Utah’s militia.