Lassen County is a county located in the northeastern part of the U.S. state of California. It was formed in 1864 and has a total area of 4,720 square miles (12,220 km2). As of the 2020 census, the population of Lassen County was estimated to be 29,633.

Cinder Cone, a 215 m (700 ft) tall volcanic cone located in the northern part of Lassen Volcanic National Park, is the youngest mafic volcano in the Lassen region and the second youngest eruption in the Twin Lakes sequence.

Eagle Lake is a lake at 5,098 ft (1,554 m) elevation in Lassen County approximately 15 mi (24 km) north of Susanville, California. An endorheic alkaline lake, it is the second largest natural lake entirely in the state of California.

The Painted Dunes are a unique natural feature located in the Lassen Volcanic National Park, in northeastern California. The dunes are situated in the Cinder Cone area of the park and are known for their striking colors, which range from deep reds and purples to bright oranges and yellows.