Riverside is a town in Okanogan County, Washington, United States. The population was 280 at the 2010 census, and increased to 329 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.