Malheur County was created Feb. 17, 1887 from the southern part of Baker County. It was named after the Malheur River flowing through the area. Peter Skene Ogden, a Hudson's Bay Company trader, referred to this river in his journal as "Riviere au Malheur" which translates as "unfortunate river." It was given this name because during an expedition into the Snake River country in 1825-1826, property and furs hidden in the area were discovered and stolen.

Malheur County is located in the southeast corner of Oregon. It is bordered by Baker County on the north, the State of Idaho on the east, the State of Nevada on the south, and Harney and Grant Counties on the west. It is the 2nd largest county in the state with 9,874 square miles.

The county seat is Vale. The 1st county courthouse was built in 1887 at a cost of $1,400. The 2nd courthouse was built in 1902 after years of rivalry between localities contending for the honor of being named the county seat. The 3rd, and current, courthouse was built in 1958.

Malheur County held its first general election in 1888 to elect a judge, sheriff, clerk, two commissioners, treasurer, assessor, superintendent of schools and coroner.

The county was first settled by miners and stockmen in the early 1860s. The discovery of gold in 1863 created interest in the area resulting in the establishment of settlements and stock ranches. Basques settled in the region in the 1890s and were mainly engaged in sheep raising. The principal industries are agriculture, livestock, food processing and tourism. The Western Treasure Valley located in the northeast corner of the county is the center of diversified and intensified farming.

The population of Malheur County steadily increased from 1890 through 1980. From 1980 to the 1990 there was a 36% decline partially due to weak agricultural seasons between 1982 and 1986. However, the 2000 population reached 31,615, representing an increase of 21.42% from 1990. The population stabilized at 31,720 in 2009, a 0.3% increase over 2000. Over half of the county's population is in the cities of Ontario, Vale and Nyssa in the Western Treasure Valley. A large number of the county's rural residents live in unincorporated areas on farms and ranches in the same valley.