The legislature of the State of Deseret created a county on January 31, 1850, to govern the civic affairs of Utah Valley, which by the 1850s was bustling with newly arrived settlers. The county name is derived from the valley name, which is derived from the Spanish name (Yuta) for the Ute Indians. The State of Deseret dissolved soon after (April 5, 1851), but the counties it had set in place continued. There is little record of any official activity conducted by the fledgling county until April 18, 1852, when a full slate of county officials was published, and recordkeeping began. The first courthouse was built in central Provo in 1866–67. It was soon outgrown and was replaced by a second courthouse (1872–73). By the 1920s, this building was also cramped, and the decision was made to erect a combined city-county building, which was completed in 1926.
The county's boundaries were adjusted in 1852, 1854, 1856, 1862, 1880, and 1884. It has retained its present boundary since 1884.