Peter Lassen, later known in Spanish as Don Pedro Lassen, was a Danish-born Californian ranchero and gold prospector. Born in Denmark, Lassen immigrated at age 30 to Massachusetts, before eventually moving to California. In California, Lassen became a Mexican citizen and received the vast Rancho Bosquejo from Governor Manuel Micheltorena. He is best known as the eponym of Lassen County, California, Lassen Peak, and Lassen Volcanic National Park.

Lassen County is a county located in the northeastern portion of the U.S. state of California. As of the 2020 census, the population was 32,730. 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, its economy now depends on employment at one federal and two state prisons; the former in Herlong and the latter two in Susanville. In 2007, half the adults in Susanville worked in one of the facilities.