Lewis Ankeny McArthur, Oregon Geographic Names (1952)
“ YAMHILL COUNTY. This county was created July 5, 1843, and now has a land area of 709 square miles according to the Bureau of the Census. It was one of the original four districts of Oregon and embraced the southwest part of the territory. Several counties have been taken from it. The origin and meaning of the name are uncertain, but the best evidence indicates that it is the white man's name for the Yamhill Indians. The Yamhill Indians were of the Kalapooian family, formerly living on Yamhill River, in Yamhill County. ”
