Yamhill County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the population was 107,722.[1] The county seat is McMinnville. Yamhill County was named after the Yamhelas, members of the Kalapuya Tribe. Yamhill County is part of the Portland-Vancouver-Hillsboro, OR-WA Metropolitan Statistical Area. It is in the Willamette Valley.

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. The county government was later (1889) moved to McMinnville where it remains today.