Lake County has been inhabited by Pomo Native Americans for over ten thousand years. Pomos had been fishermen and hunters, known especially for their intricate basketry made from lakeshore tules and other native plants and feathers. Pomo people continue to live in Lake County.
The area had European-American settlers from at least the 1840s. Lake County was created in 1861 from parts of Napa and Mendocino counties. The eastern boundary of Lake County, which was not clearly specified in the 1861 act, was clarified by legislative acts passed in 1864 and 1868. A major effect of the 1868 act was to include in Lake County the entire watershed of North Fork Cache Creek, which had previously been claimed by Colusa County.
The 1911 California Blue Book lists the major crops as Bartlett pears and beans. Other crops include grain, alfalfa, hay, prunes, peaches, apples, grapes and walnuts. Stockraising included goats, hogs, turkeys and dairying.
Some vineyards were planted in the 1870s by European Americans but the first in the state were established in the 18th century by Spanish missionaries. By the early 20th century, the area was earning a reputation for producing some of the world's greatest wines. However, in 1920, national Prohibition essentially ended Lake County's wine production. With authorized cultivation limited to sacramental purposes, most of the vineyards were ripped out and replanted with walnut and pear orchards.
The area has increased vineyard acreage from fewer than 100 acres in 1965 to more than 9,455 acres of vineyard in 2015 (a 7.6 percent increase over 2014). Lake County's grape prices, at $1,634 per ton overall, also reached an all-time high in 2015. In 2014, Lake County surpassed Mendocino County in price paid per ton of grapes in the North Coast premium market.
The number of wineries also continues to grow, with over 35 wineries now located in Lake County.
Lake County has been ranked by the American Lung Association as having the cleanest air in the nation, including in 2013, 2014 and 2015. Lake County has also been ranked twenty-four times as having the cleanest air in California. Currently, the American Lung Association's website gives Lake County air a "C" grade for high ozone days and an "A" grade for particle pollution.
Clear Lake is believed to be the oldest warmwater lake in North America, due to a geological fluke. The lake sits on a huge block of stone which slowly tilts in the northern direction at the same rate as the lake fills in with sediment, thus keeping the water at roughly the same depth. The geology of the county is chaotic, being based on Franciscan Assemblage hills. Numerous small faults are present in the south end of the lake as well as many old volcanoes, the largest being Cobb Mountain. The geologic history of the county shows events of great violence, such as the eruption of Mount Konocti and Mount St. Helena and the collapse of Cow Mountain, which created the hills around the county seat of Lakeport. Blue Lakes, Lake Pillsbury, and Indian Valley Reservoir are the county's other major bodies of water.
In the late 19th century, the worldwide popularity of mineral water for the relief of myriad physical ailments resulted in the development of mineral resorts around Clear Lake.
Greene Bartlett discovered Bartletthot springs in 1870. The springs were developed into a resort and by 1900 included a mineral water bottling plant. The resort burned down in 1934.
Harbin Hot Springs was developed by settlers in the 1860s. Harbin burned to the ground in the Valley Fire of 2015. In January 2019 it partially reopened, including the main pools and sauna, and a limited cafetaria service.
Highland Springs opened in 1891, and was destroyed by fire in 1945. During its time, Highland had an elegant dining room and a spacious hotel.
Lake County has a mediterranean climate with hot summer daytime temperatures in its lower elevations. Nighttime temperatures remain cool year-round, somewhat moderating average temperatures and relieving the summer heat.
Climate data for Clearlake, California (1981–2010 normals)
There were a total of 34,031 homes in Lake County in 2005. This county has gone through a growth in housing units, adding a sum of 1,414 residential structures since 2001, a change of 4.3 percent. Lake County ranks 978 of 3,141, compared to change in residential structure growth in counties throughout the Unities States.
Lake County had a median home value in the year 2005 of $255,300, according to the American Community Survey. This median is less than the overall California 2005 home median value of $477,700 and greater than median home value of $167,500 for the rest of the nation in that year. In 2005, the American Community Survey reported that 14.4% of Lake County's owner-occupied dwellings are valued over a half a million dollars.
In the county, the population was spread out, with 24.1% under the age of 18, 6.0% from 18 to 24, 23.6% from 25 to 44, 26.8% from 45 to 64, and 19.5% who were 65 years of age or older. The median age was 43 years. For every 100 females there were 97.6 males. For every 100 females age 18 and over, there were 94.7 males.
The median income for a household in the county was $49,627, and the median income for a family was $55,818. Males had a median income of $45,771 versus $44,026 for females. The per capita income for the county was $43,825. About 6.9% of families and 4.6% of the population were below the poverty line, including 22.8% of those under age 18 and 7.3% of those age 65 or over. (Source: U.S. Census Bureau)
The recent sharp increase in per capita income can be directly linked to those people who have recently relocated to Lake County and telecommute to their jobs in the Bay Area. In addition, real estate values have risen due to a boom from 2003 to 2006, caused by Bay Area residents' discovery that Lake County residential real estate was lower in cost than that in adjacent Napa, Sonoma and Mendocino counties.
The income of residents of the county varies widely. The county is the largest employer thus far, followed by large retailers such as Wal-Mart, Safeway, and Kmart. Several franchised retailers have recently entered the county (up 28% since 2003) and have created a diverse employment environment. Employment statistics continue to improve, again supported by the influx of Bay Area relocations and the benefit of telecommuting. Lake County is mostly agricultural, with tourist facilities and some light industry. Major crops include pears, walnuts and, increasingly, wine grapes.
According to official estimates based on the 2000 Census, 30% of housing units in Lake County were manufactured housing units. This was the highest percentage of any California county.
On November 4, 2008, Lake County voted 52.6% for Proposition 8, which amended the California Constitution to ban same-sex marriages.
Lake County was one of the few Democratic-leaning counties in California to shift toward the Republican in the 2016 Presidential Election by any substantial margin, experiencing a 14 percent swing, the second-largest in the state for either candidate, and, after Stanislaus, the closest the GOP came to flipping a county that supported Obama in 2012.
The following table includes the number of incidents reported and the rate per 1,000 persons for each type of offense.
Lake Transit serves all areas around Clear Lake. Local routes serve Lakeport, Clearlake and Lower Lake. Connections are also provided to St. Helena (in Napa County) and Ukiah (in Mendocino County). Some routes operate on weekdays only; no service is provided on Sundays and observed public holidays.
Lampson Field is the county's public airport. There are also several private airstrips located throughout the county.
In 1888 the Vaca Valley and Clear Lake Railroad reached Rumsey, but the planned line to Clear Lake was never built. The Clear Lake Railroad started work on a line from Hopland to Lakeport: "In November 1911 first ground was broken for the Hopland-Clear Lake railroad to Hopland. Mrs Harriet Lee Hammond, wife of the president of the road started construction. ... There were six miles of track out of Hopland ...", but this was also abandoned.
^Coy, Owen C. (1923). California County Boundaries: A Study of the Division of the State into Counties and the Subsequent Changes in their Boundaries. California Historical Survey Commission. Archived from the original|archive-url= requires |url= (help) on |archive-url= requires |archive-date= (help).