Sierra County is located in the Sierra Nevada of the U.S. state of California, northeast of Sacramento on the border with Nevada. The county seat is Downieville.The only incorporated city in the county is Loyalton. Sierra County was formed in 1852 and derives its name from the Sierra Nevada, Spanish word for "Snowy Range." The county has a total area of 962 mi², 99% of it is land and 1% of it is water. As of 2000, there were 3,555 people, 1,520 households, and 986 families residing in the county. The population density was 4/mi².