Winthrop is a town in Okanogan County, Washington, United States. It is east of Mazama and north of Twisp. The population of the Winthrop area was 1,916 at the 2000 census however, the incorporated town had a population of 349. The 2010 census showed an increase to 394 within the towns limits. Winthrop and Mazama recorded the coldest temperature ever measured in Washington state at −48 °F (-44.4 °C) on December 30, 1968.
Winthrop was officially incorporated on March 12, 1924. Native Americans were the first inhabitants of Winthrop. They lived along the banks of the Methow, Twisp and Chewuch rivers, digging camas root, picking berries, fishing and hunting. The first white men to visit the valley were trappers in the 1800s.
In the spring of 1868, placer gold was discovered in the Slate Creek District.