[2] The county was established in 1885 and is named for Cornelius Gilliam,[3] a colonel who commanded the forces of the provisional government of Oregon after the Whitman Massacre.

The question of a permanent county seat was placed on general election ballots in 1886, 1888, and again in 1890, when voters chose to move the county seat to Condon, known to early settlers as "Summit Springs."

The wind farm was estimated to have an economic impact of $16 million annually for Oregon.

Gilliam County is located in the central northern part of Oregon, east of the Cascade Range.

The Northern Oregon Regional Corrections Facility (Norcor), a short-term jail, serves Gilliam, Hood River, Sherman, and Wasco counties.

[14] Though Gilliam County is located in central Oregon, politically it falls in line with the eastern side of the state.

[citation needed] These numbers show a small but clear shift towards the Democratic candidate when compared to the 2004 presidential election, in which 66.3% of Gilliam Country voters voted for George W. Bush, while 32.5% voted for John Kerry, and 1.2% of voters either voted for a third-party candidate or wrote in a candidate.

This streak, however, ended in 2022 when Republican Jo Rae Perkins won most of the county's votes.

Gilliam County is in the heart of the Columbia River Plateau wheat-growing region.

The economy is based on agriculture, and wheat, barley and beef cattle are the principal products.

Transportation also contributes to the local economy; two major rivers, the John Day and Columbia, cross the area east-to-west, as does Interstate 84.

Oregon Route 19 connects the county's major cities north-to-south and provides access to the John Day Valley.