Okanogan County is a county located in the U.S. state of Washington along the Canada–US border. As of the 2010 census, the population was 41,120. The county seat is Okanogan, while the largest city is Omak. Its area is the largest in the state.About a fifth of the county's residents live in the Greater Omak Area. The county forms a portion of the Okanogan Country. The first county seat was Ruby, which has now been a ghost town for more than 100 years.
Okanogan County was formed out of Stevens County in February 1888. The name derives from the Okanagan language place name ukʷnaqín. The name Okanogan (Okanagan) also refers to a part of southern British Columbia.