Okanogan County //, also known as the Okanogan Valley, is a county located in the U.S. state of Washington. In area, it is the largest county in the state. As of the 2010 census, the population was 41,120. The county seat is Okanogan, while the largest city is Omak. Approximately 20 percent of residents live in the Greater Omak Area. The first county seat was Ruby, Washington, which has now been a ghost town for more than 100 years.
The name derives from the Okanagan language place name ukʷnaqín. The name Okanogan (Okanagan) also refers to the region that also encompasses part of southern British Columbia.
Okanogan County was formed out of Stevens County on February 2, 1888.