William Harrison Folsom (March 25, 1815 – March 19, 1901) was an architect and contractor. He constructed many of the historic buildings in Utah, particularly in Salt Lake City. Folsom is probably best known as a Latter-day Saint ("Mormon") architect. Many of his most prominent works were commissioned by The Church of Jesus Christ of Latter-day Saints (LDS Church). For a time he was sustained as the Church Architect, a calling in the church.
Folsom was born in Portsmouth, New Hampshire. By the age of 16 he held a supervisory position in his father's contracting firm. Folsom directed up to hundreds of employees on dock projects around Lake Erie. He and his father then moved to Buffalo, New York, where they ran a building business.
In New York Folsom met his future wife Zervial Eliza Clark, whom he married at age 22 on August 12, 1837. Folsom also encountered Latter Day Saint stonemason Enoch Reese, who helped convert him to Mormonism. Folsom and his wife were baptized members of the Church of Jesus Christ of Latter Day Saints in a frigid Niagara River on February 17, 1842.
Folsom and his wife traveled to Nauvoo, Illinois, in the spring of 1842. Nauvoo was then headquarters of the church, and Folsom became an acquaintance of Joseph Smith, the church's founder.
Folsom worked on the Nauvoo Temple until its completion in May 1846, when Mormons were forced from Nauvoo. He worked on the temple with Truman Angell and Miles Romney both of whom became lifelong friends. At this point Folsom moved to Keokuk, Iowa. In 1851 he traveled to the Sacramento California area to the town of Rough and Ready where he worked on water projects that were needed to mine gold. He then returned to his family in 1852.