Completing a treacherous thousand-mile exodus, an ill and exhausted Brigham Young and fellow members of the Church of Jesus Christ of Latter-Day Saints arrived in Utah’s Great Salt Lake Valley on July 24, 1847. The Mormon pioneers viewed their arrival as the founding of a Mormon homeland, hence Pioneer Day. The Mormons, as they were commonly known, left their settlement in Nauvoo, Illinois, and journeyed West seeking refuge from religious persecution. The final impetus for their trek was the murder of founder and prophet Joseph Smith on June 27, 1844.
Determined to settle in an isolated region, the pioneers made their way across the plains and over the Rocky Mountains to Utah. They lost many of their party to disease during the winter months. By the time that they reached Utah, the desolate valley was a welcome sight. Potatoes and turnips were soon planted, and a dam was built. With solemn ceremonies, the settlers consecrated the two-square-mile city, and sent back word that the "promised land" had been found. By the end of 1847, nearly 2,000 Mormons had settled in the Salt Lake Valley.
Pioneer Day is an official state holiday celebrated July 24th of every year (Utah Code). The day commemorates the Mormon pioneers passage into the Salt Lake Valley from Emigration Canyon in 1847.
The first statewide Pioneer Day celebration was held July 23-24, 1857.
July 24 is still celebrated as Pioneer Day in Utah and several other Western states. The bravery of the original settlers and their strength of character and physical endurance is commemorated with festivities including games and music, speeches, parades, rodeos, and picnics.
Source: utah.gov | loc.gov