History

The Utah territory legislature created the county on October 4, 1851 with territory not previously covered by county creations, and including some area in the future state of Nevada. It was named for thirteenth President Millard Fillmore, who was in office at the time. Fillmore was designated as the county seat. The county boundaries were altered in 1852, 1854, 1861, and in January of 1862. In July 1862, the US government created the Nevada Territory, which effectively de-annexed the described portion of Millard County falling in that Territorial Proclamation.

The county boundary was further altered in 1866, in 1888, and in 1919. In 1921 a boundary adjustment with Sevier brought Millard to its present configuration. Fillmore, located near the geographic center of the territory, was originally built as the capital of Utah Territory. The Utah Territorial Legislature approved a plan to locate the capital in the Pahvant Valley. On October 28, 1851, Utah Governor Brigham Young traveled to the valley and chose the specific site for Fillmore. The town was surveyed that same day. A colonizing company soon followed; they built house4s, a grist mill, and a sawmill. Construction of the State Capitol was initiated in 1852. The Territorial legislature met in Fillmore for the first (and only time) in 1855. The following year they voted to keep the capitol in Great Salt Lake City.