Dayton is a city in Yamhill County, Oregon, United States. The population was 2,678 at the 2020 census. The city was founded in 1850 by Andr…Dayton is a city in Yamhill County, Oregon, United States. The population was 2,678 at the 2020 census. The city was founded in 1850 by Andrew Smith and Joel Palmer. Palmer, who also served as superintendent of Indian affairs for Oregon, built a flour mill there. Dayton was named for Smith's hometown, Dayton, Ohio. Dayton post office was opened in 1851, with Christopher Taylor serving as postmaster.