[1] Its county seat is Vale,[2] and its largest city is Ontario.

The discovery of gold in 1863 attracted further development, including settlements and ranches.

Basques settled in the region in the 1890s and were mainly engaged in sheep raising.

This changed by order of the Interstate Commerce Commission on May, 13th 1923 with cities adopting train time.

Most of the county is in the Mountain Time Zone, but a small portion in the south is in the Pacific Time Zone, indicative of that area's proximity to its main service town, Winnemucca, Nevada.

[1] As of the 2010 census, there were 31,313 people, 10,411 households, and 7,149 families living in the county.

The racial makeup of the county was: 25.62% of the population were Hispanic or Latino of any race.

23.70% of all households were made up of individuals, and 12.00% had someone living alone who was 65 years of age or older.

[22] These numbers show a small shift towards the Democratic candidate when compared to the 2004 presidential election, in which 74.9% of Malheur Country voters voted for George W. Bush, while 23.8% voted for John Kerry, and 1.3% of voters either voted for a third-party candidate or wrote in a candidate.

It was one of only two counties in Oregon to give the majority of its vote to Barry Goldwater and has favored the Republican candidate for decades.

[24] The last Democratic candidate to carry the county was Franklin D. Roosevelt in 1940, and only by a margin of 29 votes.

As part of Oregon's 2nd congressional district it has been represented by Republican Cliff Bentz since 2021.

It's also within the 60th District in the Oregon House, which is represented by Republican Mark Owens.

Irrigated fields in the county's northeast corner, known as Western Treasure Valley, are the center of intensive and diversified farming.

The county's two largest employers are Heinz of Ontario, a potato processor branded as Ore-Ida, and the Snake River Correctional Institution, five miles northwest of Ontario.