Janesville (also known as Lassen) is a census-designated place in Lassen County, California. It is located 11 miles (18 km) southeast of Susanville, at an elevation of 4239 feet (1292 m). Janesville is located on the eastern slopes of the Sierra Nevada Mountain range. As of the 2010 census, it had a population of 1,408.
The community consists of an elementary school, a park, four churches, two gas stations, a pizza parlor, a coffee shop, a veterinary hospital, a hardware store, a post office, and a few other businesses.
Janesville stretches over a distance of 8 miles (13 km). Its ZIP Code is 96114. The community is inside area code 530.