Dallas is a city and the county seat of Polk County, Oregon, United States. The population was 14,583 at the 2010 census.
Dallas is along Rickreall Creek, about 15 miles (24 km) west of Salem, at an elevation of 325 feet (99 m) above sea level. It is part of the Salem Metropolitan Statistical Area.
Dallas was settled in the 1840s on the north side of Rickreall Creek and was originally named "Cynthian" or "Cynthiana". A 1947 Itemizer-Observer article states: "[T]he town was called Cynthiana after Cynthiana, Ky., so named by Mrs. Thos. Lovelady." The History of Polk County Oregon, 1987, Page 12, states: "To Mrs. Thomas J. Lovelady was given the honor of naming the new settlement and she selected the name after her home town of Cynthiana, Kentucky."
Another source claims that the origin of the name may have been Jesse Applegate's wife, Cynthia Ann. However, she lived in the Salt Creek area of northern Polk County and, according to the 1850 Federal Census, had already left Polk County by 1850.
Dallas post office was established in 1852.
In 1856, the town was moved more than a mile south because of an inadequate supply of water.
Dallas was in competition with Independence to be the county seat and the citizens of Dallas raised $17,000 in order to have a branch of the narrow gauge railroad come to their town, thus securing the honor.