The fire apparently started in one house in the early Saturday afternoon and then spread in the town of White Swan, bolstered by 40 mph winds.
The blaze raged for most of the day.
Early Sunday, Yakima County District 5 Fire Chief Brian Vogel told The Associated Press that the wild land fires had been controlled, but thousands of logs on log decks at one of the mills were still burning. They're expected to burn for another 24 hours, the Yakima Herald-Republic reported Sunday.
No residents were hurt but two firefighters were treated for minor injuries, Sgt. George Town of the Yakima County Sheriff's Office told the AP.
Some residents voluntarily evacuated and took shelter at the town's ceremonial long house and high school. Residents will be allowed to return to their homes Sunday afternoon, fire officials told the Herald-Republic.
Rural roads leading to the town, located about 35 miles southwest of Yakima, were blocked off due to the danger posed by the fire, the Yakima County Sheriff's dispatch office said.
The Yakima Herald-Republic said earlier estimates of 20 homes destroyed were downgraded Sunday to 18 homes plus some barns and buildings.
Town said Saturday night that about 70 firefighters fought the blaze, which was fueled by high winds that were expected to keep up through the night.
"We were hoping for relief from Mother Nature but it doesn't look like it right now," said Town, the department's search and rescue coordinator.
The fires spread to trees and power lines, knocking out some electricity.
"There are a lot of spot fires. We have a hazardous, dangerous situation here," Harry Smiskin, chairman of the Yakama Council, told the newspaper.
East Valley Fire Chief George Spencer said firefighters were keeping the flames from reaching the east side of Curtis Street, which bisects White Swan north to south.
Spencer told KNDO that crews were remaining on the scene overnight.
One of the homes destroyed was owned by Rodney Martin.
"I got out front and tried to water the front of the house, and it overtook me," the 45-year-old Martin told the Herald-Republic.