The United States acquired the area of Utah from Mexico in 1848. Utah Territory was organized on September 9, 1850, from the acquired area plus a small portion of territory sold to the United States by Texas. Utah Territory included all of present-day Utah, most of Nevada, and part of western Colorado and southwestern Wyoming. The territory was reduced in 1861 with the organization of Colorado and Nevada territories, and additional area was lost to Nevada in 1862 and 1866. The territory was further reduced in 1863 with the organization of Idaho Territory and in 1868 with the organization of Wyoming Territory, to arrive at generally the same boundary as the present state. Utah was admitted to the Union on January 4, 1896, as the 45th state.

Census data are available for Utah beginning with the 1850 census. The 1850 census population is for the entire area of the territory, including areas not in present-day Utah. The 1860 census population does not include the area now in Nevada, but does include portions of Utah Territory in Colorado and Wyoming, although no population was reported for the Colorado portion. The 1860 population for legally existing Utah Territory was 47,130. For an explanation of the revision to the 1870 population of Utah, see Richard L. Forstall, Population of States and Counties of the United States: 1790-1990, Washington, DC: U.S. Government Printing Office, 1996, page 162.

Data for the legally established state of Utah are available beginning with the 1900 census.