Salt Lake City was settled in 1847 by Brigham Young and his followers in The Church of Jesus Christ of Latter-day Saints, also known as the LDS Church or the Mormon Church, and whose followers are often called Mormons (originally a derogative term, now accepted and widely-used) or, less frequently (but more officially), Latter-day Saints. The Mormons migrated to the Salt Lake Valley following religious conflicts and violence in the East. The city immediately became a major transit point for people moving westward in the California Gold Rush, and the LDS Church's strong practice of missionary work drew converts primarily from Britain, Ireland, and Scandinavia to emigrate to Salt Lake City during the 1850s and 1860s in long "handcart treks", a tradition that is now ingrained in Mormon culture. This migration allowed it to become one of the largest cities in the Old West, although the conservative Church values bucked the typical Old West trend of lawless towns, sheriffs, cowboys, brothels, and rowdy saloons. Pacific Islanders are another group that was significantly recruited by the Church, and Salt Lake City possesses an unusually high Pacific Islander population. The handcart tradition ended with the arrival of the railroad in 1870, which also, with the rise of mining and industry, contributed to the first major influx of "Gentiles" (non-Mormons) into the city.

The "Utah Territory" often clashed with the U.S. government over the LDS Church's practice of polygamy. The most notable clash occurred from 1857-1858 when the government mistakenly believed that Brigham Young, the church leader and governor of the territory, planned to lead a rebellion against the government. The government then sent the military to install their own governor and maintain control over the supposed rebellious colony. Although little actual fighting took place, the event is now known as the Utah War. Brigham Young eventually conceded to their demands, although long fights over the legal status of polygamy continued through the 1880s, with statehood for Utah being denied multiple times and with the federal government passing increasingly harsher anti-polygamy laws throughout the 1870s and 1880s that landed several prominent church officials in jail. In 1890, the LDS Church prophet, Wilford Woodruff, told his members to give up polygamy, a declaration that eventually allowed Utah to achieve statehood, with Salt Lake City as its capital, in 1896.

Although the majority of Utah's residents are still members of the LDS Church (estimates generally range from 60%-70%, although the percentage of practicing members is lower), Salt Lake City itself is less than half Mormon, with some areas (especially areas dominated by ethnic minorities or more artsy areas such as the lower Avenues and Sugarhouse) being lower still.