Lassen County is a county located in the northeastern portion of the U.S. state of California. As of the 2010 census, the population was 34,895. The county seat and only incorporated city is Susanville. Lassen County comprises the Susanville, California micropolitan statistical area. A former farming, mining and lumber area, it has an economy today dependent on employment at two state and one federal prison; the former two in Susanville and the latter in Herlong. In 2007 half the adults in Susanville worked in one of the facilities.