Dayville is a city in Grant County, Oregon, United States. It was incorporated in 1913. The population was 138 at the 2000 census.
According to the United States Census Bureau, the city has a total area of 0.5 square miles (1.3 km2), all land.
The city is 125 miles (201 km) east of Bend, Oregon, in the John Day valley, at the confluence of the main stem of the John Day River with the South Fork John Day River. Main Street in Dayville is U.S. Route 26, lined with large cottonwood trees.