The first known traverse by non-Indians was made by Fathers Domínguez and Escalante (1776), as they sought to establish a land route between California and Spanish America.

[4] The region was claimed by the Spanish Empire as the Alta California division of New Spain (1521-1821) and was later under Mexican control (1821-1848).

Neither the Spanish Empire nor Mexico ever had a major presence in the area and their practical control was nominal.

In 1831-32 Antoine Robidoux, a French trapper licensed by the Mexican government established a trading post near present-day Whiterocks.

In 1861 Young dispatched an exploring party to the Uinta Basin; they reported "that section of country lying between the Wasatch Mountains and the eastern boundary of the territory, and south of Green River country, was one vast contiguity of waste and measurably valueless."

Young made no further effort to establish communities in the area but nonetheless included it in their proposed State of Deseret.

They established the county seat at Ashley, a now-abandoned settlement three miles north of the present courthouse in Vernal.

The northern boundary of Uintah County originally extended to the north border of Utah.

In 1918, the extreme northern portion (lying north of the Uinta Mountain watershed divide) was split off to form Daggett County.

Ten miles farther downstream, it is joined by Willow Creek, flowing northward from the lower part of the county.

[8] The county terrain slopes to the south and to the west, with its highest parts found on the crests of the Uinta Mountains, running east–west across the northern border.

The county's geography ranges from high mountain terrain (Uinta Mountains) to the fertile Ashley Valley (site of the county seat), to a rugged and desolate canyonland which includes the Dinosaur National Monument, to desolate and largely uninhabited hills in the south ("The Bookcliffs" to locals; officially Roan Plateau).

There is some agriculture in Uintah County, primarily focusing on raising cattle and sheep and cultivating alfalfa.

In addition to the large Visitor Center at the Monument's Jensen site, a natural history museum, the Utah Field House of Natural History State Park Museum, showcasing some of the area's finds, was established in Vernal by the State of Utah.