Susanville is the only incorporated city in Lassen County, California, in the United States. It serves as the county seat and is situated on the Susan River in the southern part of the county at an elevation of 4,186 feet (1,276 meters).
As of the 2020 census, the city has a population of 16,728, reflecting a decrease from its 2010 population of 17,947. The Susanville urban area specifically comprises 4,233 households and a population of 8,995 people.