The first Euro-American settlers arrived in what would become Utah on July 24, 1847, which is now commemorated as Pioneer Day in the state.
These settlers, Mormon pioneers led by Brigham Young, appealed to the United States Congress for statehood in 1849, asking to become the State of Deseret.
Their proposal was denied, but they received some recognition in September 1850 when the U.S. Government created the Territory of Utah as part of the compromise of 1850.
A territorial assembly, known as the Utah Territorial Legislature, was created to be the governing body for the territory.
The assembly met in various buildings including the Council House, which had originally been constructed to serve as capitol of the provisional State of Deseret, until the first capitol building was constructed.

One of the first official acts of the assembly was to designate a capital city for the territory.
On October 4, 1851, Millard County and its capital of Fillmore were created in the empty Pavant Valley for this purpose.
The area was named for then current president Millard Fillmore.
Its centralized location in the territory made it seem an  ideal place for Utah's capital city.
Construction started on Utah's first capitol building, known as the Utah Territorial Statehouse, the next year.
The building was designed by LDS Church Architect Truman O. Angell, and was funded with $20,000 (equivalent to $488 thousand in 2018) appropriated by the United States Congress.
 The $20,000 was insufficient to pay for the capitol as designed, and so only the south wing was completed.
In December 1855, the fifth Utah Territorial Legislature met in the building (it would be the first and only complete session in Fillmore).
The next year the sixth Utah Territorial Legislature once again met in the statehouse, but the session was relocated to Salt Lake City after legislators complained about the lack of housing and adequate facilities in Fillmore.
As a result, in December 1856 Salt Lake City was designated Utah's capital, and the statehouse in Fillmore was abandoned.
Several buildings in Salt Lake City then served as temporary homes for the state legislature and offices for state officers, including the previously used Council House, and beginning in 1866, the Salt Lake City Council Hall.
The first Euro-American settlers arrived in what would become Utah on July 24, 1847, which is now commemorated as Pioneer Day in the state. These settlers, Mormon pioneers led by Brigham Young, appealed to the United States Congress for statehood in 1849, asking to become the State of Deseret. Their proposal was denied, but they received some recognition in September 1850 when the U.S. Government created the Territory of Utah as part of the compromise of 1850. A territorial assembly, known as the Utah Territorial Legislature, was created to be the governing body for the territory. The assembly met in various buildings including the Council House, which had originally been constructed to serve as capitol of the provisional State of Deseret, until the first capitol building was constructed.
One of the first official acts of the assembly was to designate a capital city for the territory. On October 4, 1851, Millard County and its capital of Fillmore were created in the empty Pavant Valley for this purpose. The area was named for then current president Millard Fillmore. Its centralized location in the territory made it seem an  ideal place for Utah's capital city. Construction started on Utah's first capitol building, known as the Utah Territorial Statehouse, the next year. The building was designed by LDS Church Architect Truman O. Angell, and was funded with $20,000 (equivalent to $488 thousand in 2018) appropriated by the United States Congress.  The $20,000 was insufficient to pay for the capitol as designed, and so only the south wing was completed. In December 1855, the fifth Utah Territorial Legislature met in the building (it would be the first and only complete session in Fillmore). The next year the sixth Utah Territorial Legislature once again met in the statehouse, but the session was relocated to Salt Lake City after legislators complained about the lack of housing and adequate facilities in Fillmore. As a result, in December 1856 Salt Lake City was designated Utah's capital, and the statehouse in Fillmore was abandoned. Several buildings in Salt Lake City then served as temporary homes for the state legislature and offices for state officers, including the previously used Council House, and beginning in 1866, the Salt Lake City Council Hall.
Utah State Capitol