Yamhill County is also the center of Oregon's wine industry, having the largest area of any Oregon county planted in vineyards. Six of the state's American Viticultural Areas are wholly or partly in the county: Chehalem Mountains AVA, Dundee Hills AVA, Eola-Amity Hills AVA, McMinnville AVA, Ribbon Ridge AVA, and Yamhill-Carlton District AVA. Over 80 wineries and 200 vineyards represent the largest concentration of wine growers and producers in any county in the state. Pinot Noir produced in the county rivals the best in the world. Others varieties grown include Pinot Gris, Pinot Blanc, Chardonnay, Riesling, and Gewürztraminer.
The tallest mountain in the county is Trask Mountain in the northwest corner of the county.
There were 28,732 households out of which 37.40% had children under the age of 18 living with them, 60.00% were married couples living together, 9.90% had a female householder with no husband present, and 25.60% were non-families. 19.70% of all households were made up of individuals and 8.40% had someone living alone who was 65 years of age or older. The average household size was 2.78 and the average family size was 3.17.
In the county, the population was spread out with 26.90% under the age of 18, 11.40% from 18 to 24, 28.50% from 25 to 44, 21.40% from 45 to 64, and 11.70% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 102.20 males. For every 100 females age 18 and over, there were 101.30 males.
The median income for a household in the county is $44,111, and the median income for a family was $50,336. Males had a median income of $35,686 versus $25,254 for females. The per capita income for the county was $18,951. About 6.00% of families and 9.20% of the population were below the poverty line, including 10.10% of those under age 18 and 7.50% of those age 65 or over.
The earliest non-native settlers were employees of the various fur companies operating in Oregon Country, who started settling there around 1814. But it was the establishment of the Oregon Trail that led to significant migration to the area.
Yamhill County was created in 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 over , 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. The county government was later (1889) moved to McMinnville where it remains today.
The Mount Hebo Air Force Station was a Cold War air defense installation from 1956 to 1980. Located next to Tillamook County, at the top of 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.