On February 4, 1841, the Nauvoo Legion was officially organized as an independent militia attached to the Illinois State Militia. Joseph Smith was elected Lieutenant General in command. The Saints wished for
their own militia unit because of the harsh experiences of Missouri.
Organized with two “cohorts,” the First Cohort was mounted infantry, and the Second Cohort was infantry, rifles, and artillery. Legion membership topped 3,000 men by 1844. Although the Legion was meant for protection, its size caused fear in neighboring communities, leading to bad decisions by both Mormons and their neighbors.
The Nauvoo Legion performed active duty in June 1844. On June 10, the Legion was called out to assist the city marshal in the destruction of the Nauvoo Expositor press. This act, backed up by an armed militia, inflamed tensions. Within days, armed groups wandered the prairie looking for a fight.
When Joseph Smith, as mayor, declared martial law within city limits on June 18, he called on the Legion to defend the city. His last speech was to the Nauvoo Legion that day.
After Joseph and Hyrum Smith were killed, the Legion played ceremonial roles in their funeral—escorting the remains and the band playing music during the viewing.
Their involvement in the destruction of the Expositor and enforcing martial law stoked fears of how dangerous a large militia could be. Heeding a general outcry, the State of Illinois officially disbanded the Nauvoo Legion on January 29, 1845.