In 1857 they were forced to migrate to the Grand Ronde Indian Reservation created in Oregon's Coastal Range two years earlier.

The earliest non-native settlers were employees of the various fur companies operating in Oregon Country, who started settling there around 1814.

Yamhill District (later county) was created on July 5, 1843, five years before the Oregon Territory was established.

It was one of the original four districts created by Oregon's first Provisional Legislature, along with Twality (later Washington), Clackamas, and Champooick (later Marion) counties.

The district was originally spread over 12,000 square miles (31,000 km2), an area that was broken up into twelve present-day counties.

Lafayette, the principal trading center of the western Willamette Valley in early Oregon history, was made the county seat in 1847.

Located next to Tillamook County, at the top of 3,154-foot (961 m) high Mount Hebo, Air Force radars operated by the 689th Radar Squadron and the 14th Missile Warning Squadron were essential parts of the nation's integrated air defenses.

The large radomes protecting the radars from adverse weather effects could be seen silhouetted against the sky from many parts of Yamhill County.

In 1900 the Yamhill River lock and dam was completed about 1.5 miles (2.4 km) downriver from Lafayette, Oregon.

No Democratic presidential candidate has won Yamhill County since Lyndon Johnson's 1964 landslide, and the only other Democrats to carry the county since Oregon's statehood have been Franklin Roosevelt in 1940, 1936 and 1932, along with Woodrow Wilson in 1912 when the Republican vote was divided.

Express Employment Professionals, Stoller Family Estates, and Xenium are the lead sponsors for the upcoming 2020 Air Show.

Yamhill County's economy is supported largely by its many unionized facilities such as Cascade Steel in McMinnville and Decommissioned White Birch Paper now owned by WestRock in Newberg.

[citation needed] This agricultural production includes wheat, barley, horticulture, and dairy farming, with 13,201 acres or 53.42 square kilometres in 1997 planted in orchards.

Over 80 wineries and 200 vineyards represent the largest concentration of wine growers and producers in any county in the state.

Yamhill County Institutions of Higher Education (IHEs) include Linfield University and Chemeketa Community College McMinnville Campus, along with George Fox University and Portland Community College in Newberg.