William Bowker Preston, a native of Virginia, was born in 1830. In 1852, he went to California and eventually settled in Yolo County as a farmer. His neighbors were the Thatchers, an LDS family. By 1857, Preston had fallen in love with Harriet Thatcher, and in February of that year he was baptized into the LDS Church. Preston was soon called by George Q. Cannon to serve in the Pacific Coast mission. The earliest letters in the collection are to his sweetheart Harriet while on this mission. Preston asked for Harriet's hand in marriage, but her father, Hezekiah Thatcher, refused to allow the union. In the fall of 1857 California LDS were called back to Utah to assist in defending the territory against the U.S. Army. Preston, the Thatchers, and other LDS families arrived in Salt Lake City in January 1858. Preston and Harriet were married in February 1858 and first settled in Payson, Utah where Preston built an adobe house. However, in August 1859, the Prestons and the Thatchers moved to Cache Valley and in November Preston was named bishop of Logan.

In April 1865, Preston was called to serve a mission in Europe. Upon arrival in Liverpool, England, Preston was assigned to Newcastle and Durham. In January 1866, he was called to serve in the Liverpool office, which at that time was the headquarters of the European Mission. Preston's two mission diaries, and the complementary letters to Harriet, give rich, full details of his daily activities in the field of labor and in the mission office, i.e., office traffic (composition of office employees, names and assignments of missionaries, visits of Church authorities from the U.S., etc), full detail on emigration (for which he had specific responsibility), and his many travels to visit branches of the Church in England, Wales, and Scotland. In August 1867, Preston visited the Paris Exposition. He was released from his mission in the summer of 1868 and sailed from Liverpool in charge of 600 emigrating Saints.

Upon his return home, Preston resumed his duties as bishop in Logan and was elected to the territorial legislative assembly (1872-1882) where he had also served in the 1860s. He also took a leading part in the construction of the Utah and Northern Railroad. In 1871, he was appointed presiding bishop of Cache Valley (a regional bishop with jurisdiction over twenty wards). In 1877, he was called to the Cache Valley stake pPresidency, serving as counselor to his brother-in-law, Moses Thatcher. In 1879, Preston was called as Cache Valley stake president, and in 1883 vacated that office to assume the responsibilities of the Presiding bishop of the Church. He was released in December 1907 due to poor health and died in August 1908.