Crook County was established on October 24, 1882. It was created from the southern part of Wasco County and named after U.S. Army Major-General George Crook, a hero of the Snake Indian Wars.

Crook County is situated in the geographic center of Oregon. It has been reduced from its original size of 8,600 square miles to 2,986 square miles by the creation of Jefferson County in 1914 and Deschutes County in 1916. The current boundaries were established in 1927. Crook County is bounded by Jefferson and Wheeler Counties to the north, Grant and Harney Counties to the east, and Deschutes County to the south and west.

In 1882 the Legislative Assembly established Prineville as the county seat. The voters confirmed the choice of Prineville, the only incorporated town in the county, in the 1884 general election. Prineville was named in honor of the town's first merchant, Barney Prine.

The first courthouse was a one story wooden structure at the corner of West 5th and Main Streets. In 1885 a two story wooden structure was built for $5,474. By 1905 this building was considered unsafe to store the county's records, and a $16,526 bid was accepted to erect a new, brick and stone courthouse. The building was completed in 1909, at a cost $48,590, and remodeled in the early 1990s.

The government of Crook County consisted originally of a county judge, two county commissioners, clerk, treasurer, and sheriff. The position of school superintendent appeared by 1899. The county also added an assessor.

The first census in 1890 showed a population of 3,244 excluding the Indians. There has been a fluctuation in the population's growth. The last several censuses have shown an increase in inhabitants with the 2000 population given at 19,182 representing a 35.94% increase from 1990.

Routes over the Cascades were difficult to find and traverse, thus delaying development in the area until access was more developed. The first effort was in 1862 when a supply train with cattle crossed the Scott Trail. This was also the first group of non-natives to spend the winter in central Oregon. The discovery and development of the Santiam Pass in the 1860s made development of the area much easier. The economy of the county is based on agriculture and forestry. Agriculture is supported by the development of irrigation districts, which permits the raising of hay, grain, mint, potatoes, and seed. Range and forest lands allow grazing for a sizable livestock industry. The Ochoco National Forest's stand of ponderosa pine is the main source of lumber. As the lumber industry suffers with restricted log cutting, tourism and recreation are helping to strengthen the economy.