South Lake Tahoe is the most populous city in El Dorado County, California, United States, in the Sierra Nevada mountains. The city's population was 21,330 at the 2020 census, down from 21,403 at the 2010 census. The city, along the southern edge of Lake Tahoe, extends about 5 miles west-southwest along U.S. Route 50, also known as Lake Tahoe Boulevard.