The murder of Joseph Smith by a mob in Carthage, Illinois, in 1844 left the Latter-day Saint movement he founded without a settled home and increasingly at odds with its neighbors. Brigham Young, who emerged as the movement's leader, organized a mass exodus west beginning in February 1846, aiming for territory then outside United States jurisdiction where the church could govern its own affairs. An advance company, with Young himself ill and carried partway by wagon, reached the Salt Lake Valley on July 24, 1847, a desert basin most other American settlers had passed over as unpromising. Young is remembered as declaring, on first seeing the valley, that it was the right place, and the pioneers began irrigating and planting within days.
The city they laid out followed a plan Joseph Smith had drafted years earlier for an ideal religious community, the Plat of Zion: wide streets aligned to the compass, large blocks divided into generous house lots, and a central temple block, all intended to let a self-sufficient agricultural population live inside an orderly city rather than scattered across the land. Salt Lake City's downtown grid still follows that layout, and the numbered street system radiating from Temple Square remains one of the most legible examples of planned nineteenth century American town design.