[5] The original site of the Dayville post office was 3 miles (5 km) west of the city's current location.

[5] In the mid-19th century, Dayville was along the route of a wagon road, renamed The Dalles Military Road in about 1870, that connected The Dalles on the Columbia River with gold mines near Canyon City.

[7] The city is 125 miles (201 km) east of Bend and 233 miles (375 km) southeast of Portland,[8] at the confluence of the John Day River with the South Fork John Day River.

Murderers Creek State Wildlife Area, the Aldrich Mountains, and parts of the Malheur National Forest are slightly southeast of Dayville.

The Sheep Rock Unit of the John Day Fossil Beds National Monument, including the Thomas Condon Paleontology Center and the James Cant Ranch Historic District and museum, are 2 miles (3 km) north of Picture Gorge along Route 19.

[10] According to the United States Census Bureau, the city has a total area of 0.53 square miles (1.37 km2), all land.

The racial makeup of the city was 96.38% White, 2.17% Native American, 0.72% Asian, and 0.72% from two or more races.

[8] The Dayville Presbyterian Church[16] has since the 1970s offered hospitality to bicyclists journeying along the TransAmerica Bicycle Trail.