Keystone is a census-designated place (CDP) in Summit County, Colorado, United States. The population was 825 at the 2000 census. The Dillon Post Office (ZIP Code 80435) serves Keystone postal addresses.
Keystone is the home of the Keystone Resort. Originally constructed in the 1970s by the Ralston Purina Company, it is now owned by Vail Resorts. The Keystone Resort ski area occupies 3 separate mountains. The resort has several summer and winter outdoor activities. The winter activities include skiing, snowboarding, ice-skating, cross-country skiing, dog sleigh, and snowmobiling. The summer activities include hiking, biking, fishing, golf and trail running.