Winthrop is a town in Okanogan County, Washington, United States. It is east of Mazama and north of Twisp. The population was 394 at the 2010 census, and increased to 504 at the 2020 census.

Okanogan County is a county located in the U.S. state of Washington along the Canada–U.S. border. As of the 2020 census, the population was 42,104. The county seat is Okanogan, while the largest city is Omak. Its area is the largest in the state.