There are 10 US Post Offices in Yamhill County serving a total of 99,452 residents equating to 9,945 residents per post office. It's estimated that approximately 158,736 packages are handled across the 10 county post offices annually. Yamhill County is a county located in the U.S. state of Oregon. As of the 2010 census, the population was 99,193. The county seat is McMinnville. The origin of the name is probably from an explorer's name for a local Native American tribe, the Yamhill, who are part of the North Kalapuyan family. Yamhill County is included in the Portland-Vancouver-Hillsboro, OR-WA Metropolitan Statistical Area. It is located in the Willamette Valley."