Due to discontent in Missouri, Joseph Smith moved his followers to Nauvoo, Illinois in 1839. In June of 1844, Smith and his brother were killed by a mob, and the following year the state of Illinois revoked the city charter for Nauvoo. Brigham Young, the new leader, organized an evacuation of Nauvoo under the threat of federal troops. They moved to camp at Sugar Creek.
By March of 1846, Sugar Creek was home to 3,000 people and 500 wagons. Young divded them into 3 companies of 100 families each, each company with its own captain. In June of 1846 10,000 of the followers had reached Council Bluffs, Iowa. They crossed Iowa averaging 2-3 miles per day and so had to winter in camp at Winter Quarters (near Omaha), Nebraska, before crossing the Rockies. The population of Winter Quarters was about 5,000, and 400 people had died by the Spring of 1847.
In April, 1847, Young took 150 people with him across Nebraska, Wyoming, and into the Great Salt Lake basin. This trip took over 100 days. In November Young returned to Winter Quarters and spent the Winter preparing the remaining followers to travel into what would become Salt Lake City.