The Mormon Trail is the 1,300-mile (2,100 km) route from Illinois to Utah on which Mormon pioneers (members of the Church of Jesus Christ of Latter-day Saints) traveled from 1846 to 1869. The Mormon Trail is a part of the United States National Trails System, known as the Mormon Pioneer National Historic Trail.

The Mormon Trail extends from Nauvoo, Illinois, which was the principal settlement of the Latter Day Saints from 1839 to 1846, to Salt Lake City, Utah, which was settled by Brigham Young and his followers beginning in 1847. From Council Bluffs, Iowa to Fort Bridger in Wyoming, the trail follows much the same route as the Oregon Trail and the California Trail; these trails are collectively known as the Emigrant Trail.

The Mormon pioneer run began in 1846 after Young and his followers were driven from Nauvoo. They left with the aim of establishing a new home for the church in the Great Basin and crossed Iowa. Along their way, some were assigned to establish settlements and to plant and harvest crops for later emigrants. During the winter of 1846–47, the emigrants wintered in Iowa, other nearby states, and the unorganized territory that later became Nebraska, with the largest group residing in Winter Quarters, Nebraska. In the spring of 1847, Young led the vanguard company to the Salt Lake Valley, which was then outside the boundaries of the United States and later became Utah.

During the first few years, the emigrants were mostly former occupants of Nauvoo who were following Young to Utah. Later, the emigrants increasingly included converts from the British Isles and Europe. The trail was used for more than 20 years, until the completion of the first transcontinental railroad in 1869. Among the emigrants were the Mormon handcart pioneers of 1856–60. Two of the handcart companies, led by James G. Willie and Edward Martin, met disaster on the trail when they departed late and were caught by heavy snowstorms in Wyoming.

Under the leadership of Joseph Smith, Latter Day Saints established several communities throughout the United States between 1830 and 1844, most notably in Kirtland, Ohio; Independence, Missouri; and Nauvoo, Illinois. However, the Saints were driven out of each of these settlements in turn, due to conflicts with other settlers. This included the actions of Missouri Governor Lilburn Boggs, who issued Missouri Executive Order 44, which called for the "extermination" of all Mormons in Missouri. Latter-day Saints were finally forced to abandon Nauvoo in 1846.

Although the movement had split into several denominations after Smith's death in 1844, most members aligned themselves with Brigham Young. Under Young's leadership, about 14,000 Mormon citizens of Nauvoo set out to find a new home in the West.

Following the succession crisis, Young insisted the Mormons should settle in a place no one else wanted and felt the isolated Great Basin would provide the Saints with many advantages.

Young reviewed information on the Great Salt Lake Valley and the Great Basin, consulted with mountain men and trappers, and met with Father Pierre-Jean De Smet, a Jesuit missionary familiar with the region. Young also organized a vanguard company to break trail to the Rocky Mountains, evaluate trail conditions, find sources of water, and select a central gathering point in the Great Basin. A new route on the north side of the Platte and North Platte rivers was chosen to avoid potential conflicts over grazing rights, water access, and campsites with travelers using the established Oregon Trail on the river's south side.^{[citation needed]}