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.

[9] Lassen was one of General John C. Fremont's guides, and a famous trapper, frontiersman, and Indian fighter.

Gold was discovered at Hayden Hill, and the small town developed to support the miners.

Hayden Hill no longer exists: when the mining stopped, the townspeople left for other communities.

In the 1890s many immigrant family groups arrived in the county, primarily coming from Lincolnshire and Herefordshire, England as well as the towns of Belgrade, Novi Sad, Niš and Kragujevac in Serbia.

A pro-German newspaper editor from San Francisco noted that "the inhabitants of Lassen County" were "sympathetic to Britain, hostile to Germany, and indifferent to France.

"[13][14][10][15] A narrow gauge railroad, the Nevada-California-Oregon Railway, ran through Lassen County from 1880 to 1927.

As this railroad was completed, the Red River Lumber Company set up shop,[8] building the town of Westwood, California, to support its massive logging operation.

Since the late 20th century, three prisons have been opened in and near Susanville: California Correctional Center (minimum security, 1963) and High Desert State Prison (California) (maximum security, 1995), both in the city; and the nearby Federal Correctional Institution, Herlong (opened 2007).

[6] In "job-starved rural America, ... residents see them [prisons] as the last and only chance for employment after work at the lumber mill or the dairy dries up.

[17] Part of Lassen Volcanic National Park extends onto a western corner of the county.

From 1980 on, however, it has been overwhelmingly Republican in presidential and congressional elections, coinciding with the dominance of the prisons in local employment.

In 2016, 2020, and 2024, Lassen stood as Donald Trump's best county in the state, giving him a 50% or greater margin over overwhelming statewide winners Hillary Clinton, Joe Biden, and Kamala Harris.

Lassen County is in California's 1st congressional district, represented by Republican Doug LaMalfa.

[41] The following table includes the number of incidents reported and the rate per 1,000 persons for each type of offense.