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.

Chelan County () is a county in the U.S. state of Washington. As of the 2010 census, its population was 72,453. The county seat and largest city is Wenatchee. The county was created out of Okanogan and Kittitas Counties on March 13, 1899. It derives its name from a Chelan Indian word meaning "deep water," likely a reference to 55-mile (89 km)-long Lake Chelan, which reaches a maximum depth of 1,486 feet (453 m). Chelan County is part of the Wenatchee, Washington, Metropolitan Statistical Area.

Washington, officially the State of Washington, is a state in the Pacific Northwest region of the Western United States. Named for George Washington—the first U.S. president—the state was formed from the western part of the Washington Territory, which was ceded by the British Empire in 1846, in accordance with the Oregon Treaty in the settlement of the Oregon boundary dispute. .