Fillmore was Utah's first territorial capital and was named for U.S. President Millard Fillmore in recognition of his courage in appointing Brigham Young Utah's first territorial governor. On 4 October 1851 the Utah territorial legislature passed a joint resolution creating Millard County from a portion of Iron County known as "Pahvant Valley"; they named its county seat Fillmore City. This resolution also relocated the territorial capital to the new community and appropriated $20,000 toward that effort. On 21 October two companies set out from Salt Lake City for the Pahvant Valley. Brigham Young headed a delegation of lawmakers making the site selection of the territorial capital. The other company, under the direction of Anson Call, was chosen to make a settlement. On 28 October territorial lawmakers selected a spot located on the hunting grounds of the Pahvant Indians, 150 miles south of Salt Lake City.
A monumental statehouse was planned to be constructed to house the territorial government. Truman O. Angell, architect of the Salt Lake Temple, designed an elaborate structure of four wings in the form of a cross with a Moorish dome at the center. Local red sandstone and native timber were to be used in its construction. The first wing was completed for the fifth annual session of the Utah territorial legislature which convened in Fillmore on 10 December 1855. The sixth legislative session also met at Fillmore, but soon adjourned to reconvene in Salt Lake City. Because the development of southern Utah was slow and accommodations in Fillmore inadequate, the capital was moved to Salt Lake City. The statehouse was never completed, but the first wing remains Utah's oldest governmental building and now serves as a state museum.
Anson Call and thirty families began the settlement of Fillmore City. By February 1852, about thirty houses and a log schoolhouse were completed in the form of a fort. In 1852 a post office was established, and by 1853 the population of Fillmore was listed as 304. Farming and stock raising quickly became its principal industries. Because of Indian problems, a fort was constructed in 1853-54 of stone and adobe, and all local people were located within its walls for safety. On 26 October 1853 a team of U.S. Army topographical engineers headed by Lieutenant John W. Gunnison was massacred by Pahvant Utes not far from Fillmore. Seven were killed.
The first settlers were principally American, but later an influx of English, Scots, Welsh, and Scandinavians arrived in the area. Today, Fillmore is a community of 1,956 people. It is a tightly knit community which has won numerous beautification awards and is dedicated to community development. It is the home of the Chief Kanosh Pageant as well as one of the largest Fourth of July celebrations in Utah. Its citizens are strong supporters of high school athletics. In 1985 the former Fillmore Hospital was purchased by Fillmore City, and by the fall of 1986 it had been remodeled, with city offices in the east wing and the President Millard Fillmore Library in the west wing. Fillmore is also the home of a multimillion-dollar mushroom plant located in the city's industrial park where 100,000 pounds. of mushrooms are harvested each week. During the 1980s, Cambodian and Vietnamese immigrants began to work in the mushroom factory.