Benton County was created on December 23, 1847, by an act of the Provisional Government of Oregon.

[3] The county was named after Democratic Senator Thomas Hart Benton of Missouri, an advocate of the doctrine of Manifest Destiny and the belief that the American government should control the whole of the Oregon Country.

[4] The county was created out of lands originally inhabited by the Klickitat, who rented it from the Kalapuyas for use as hunting grounds.

All aboriginal claims to land within Benton County were ceded in the Treaty of Dayton in 1855.

[12] In terms of ethnicity, 22.6% reported German ancestry, 16.1% English, 13.5% Irish, and 3.6% were American heritage.

[16] (As of 2023) For a long time, Benton County strongly favored the Republican Party due to its significant Yankee influence.

In the 1932 presidential election, it was the only county in the state to vote for Herbert Hoover instead of FDR.

In 1964, Lyndon Johnson became the first Democrat to win an absolute majority of the county's vote since Horatio Seymour.

This is largely due to the leanings of Oregon State's student body and staff, closely tracking with Democratic gains in other counties influenced by college towns.

[19] The voters have chosen to eliminate the traditional elected county offices of Assessor, Treasurer, Surveyor, Justice of the peace, and Clerk.

[20][21] The three current Benton County Commissioners are Chair Pat Malone, Xanthippe Augerot, and Nancy Wyse.

He was appointed to the office in March 2021 to fill the remainder of the term of retiring sheriff Scott Jackson.

Along with Oregon State University, agriculture, lumber, wood products, and some printing technology research and development form the economic base of the county.

A substantial portion of the nation's research in forestry, agriculture, engineering, education and the sciences takes place at OSU.