what county is susanville, ca located in
Susanville, California. Susanville (formerly known as Rooptown) is the county seat of Lassen County, California, United States. Susanville is located on the Susan River in the southern part of the county, at an elevation of 4,186 feet (1,276 m). The population was 17,974 in the 2010 census, up from 13,541 in the 2000 census.