San Luis Obispo County (), officially the County of San Luis Obispo, is a county on the Central Coast of California. Its population was 282,424 at the 2020 census, and the U.S. Census Bureau estimated 282,367 residents on July 1, 2025. San Luis Obispo is the county seat and its largest city by population. The county has of land, extending from the Pacific coast across the Santa Lucia Range to inland valleys and the Caliente Range.
The county was established in 1850. Its history includes Chumash and Salinan communities, Spanish missions, Mexican ranchos, and the development of agriculture, railroads, and coastal shipping. Cal Poly opened in 1903, and military training installations expanded during World War II.
Service industries account for most employment, including government, education and health care, and leisure and hospitality. Agriculture includes strawberries and wine grapes, the county’s two highest-value crops in 2024. The county is also home to Hearst Castle and Diablo Canyon Power Plant.
History Indigenous history Archaeological evidence documents thousands of years of coastal occupation in what is now San Luis Obispo County. Excavations around Morro Bay have identified fishing communities dating to the Millingstone Horizon. Chumash communities lived around Morro Bay and Los Osos, while Salinan communities inhabited the vicinity of present-day San Miguel.
Historical accounts disagree about the boundary between Northern Chumash and Salinan languages along the northern coast of the county. Mission registers and later ethnographic records leave the locations and linguistic affiliations of many villages uncertain.
The Yak titʸu titʸu yak tiłhini Northern Chumash Tribe and the Salinan Tribe continue cultural preservation work in the region.
Spanish missions and Mexican ranchos Junípero Serra founded Mission San Luis Obispo de Tolosa on September 1, 1772. Mission San Miguel Arcángel followed on July 25, 1797, founded by Fermín Lasuén. Spanish missions depended on Indigenous agricultural and ranching labor. Introduced diseases reduced Chumash populations, while livestock grazing depleted traditional plant foods and colonial authorities suppressed Indigenous burning. In 1803, the viceroy of New Spain ordered baptized Indigenous people to leave their villages and reside at the missions.
Mexican secularization began in 1834. Regulations provided for distributing land and livestock to Indigenous mission residents, but much of the property instead passed into private ranchos. In 1839, Indigenous residents of Mission San Luis Obispo sought to retain Corral de Piedra, where they kept cattle. Governor Juan Bautista Alvarado granted the ranch and its cattle to José María Villavicencio in 1840. Rancho San Miguelito, granted to Miguel Ávila in 1842, included the future Diablo Canyon site.
Between 1837 and 1843, some Salinan, Northern Chumash, and Yokuts families remained near the former missions, while others became ranch workers. In 1844, Governor Manuel Micheltorena granted land at Las Gallinas, El Nacimiento, and La Estrella to Indigenous residents of San Miguel. U.S. courts later rejected those grants on the grounds that required improvements had not been made.
County formation and transportation Mexico ceded California to the United States under the 1848 Treaty of Guadalupe Hidalgo, which ended the Mexican–American War. San Luis Obispo County was one of California’s original counties, established in 1850.
The federal Land Act of 1851 required holders of Spanish and Mexican land grants to submit claims to a land commission. Claimants bore the costs of litigation and surveys, and confirmation could take decades. Rancho San Miguelito received its U.S. patent in 1877.
Cattle ranching and farming dominated the nineteenth-century economy. The drought of 1862–1864 forced the sale of many cattle ranches and encouraged a shift toward dairying.
Coastal wharves and steamship service connected farms to outside markets. Chinese immigrants worked on railroads, roads, and wharves. Southern Pacific reached San Miguel and Paso Robles in 1886 and San Luis Obispo in 1894; completion of the coastal line in 1901 connected the county by rail to both San Francisco and Los Angeles.
Early twentieth century and World War II The California Polytechnic School, now Cal Poly, was established by state legislation in 1901 and opened in 1903, initially teaching agriculture, engineering, and household arts.
Oil storage and shipping developed at Port San Luis as production expanded in the neighboring Santa Maria fields. In 1906, Union Oil connected those fields to a storage facility at the port by pipeline.
William Randolph Hearst and architect Julia Morgan developed Hearst Castle above San Simeon between 1919 and 1947. The estate was given to the state in 1958.
Japanese immigrant farmers cultivated vegetables and flower seeds during the early twentieth century. In 1942, Japanese Americans in the county were forcibly removed to incarceration camps; some returned after the war, while others did not.
Camp San Luis Obispo, established in 1927, expanded during World War II. Camp Roberts began training troops in March 1941.
Postwar growth and environmental disputes After World War II, veterans who had trained locally settled in the county, and educational opportunities at Cal Poly attracted others. Housing demand led to the conversion of farmland around existing towns into residential subdivisions.
From the 1970s, agriculture shifted toward wine grapes, vegetables, fruit, and seed crops, while service and professional employment expanded.
Construction of Diablo Canyon Power Plant became a focus of environmental opposition during the 1970s and 1980s, including campaigns by San Luis Obispo Mothers for Peace and the Abalone Alliance. The plant’s two reactors began commercial operation in 1985 and 1986. In 1986, voters approved Measure A, requiring voter approval for onshore facilities serving offshore oil development.
Geography
According to the U.S. Census Bureau, the county has a total area of , of which is land and (comprising 8.7%) is water.
The La Panza, Garcia, and Santa Lucia ranges occupy the central portion of the county, and the Caliente Range lies in the southeast. The Santa Lucia Range extends along much of the western county, rising sharply from the coast in the north. The Irish Hills lie between Los Osos and Avila Beach. Caliente Peak reaches , the county’s highest elevation.
The Salinas River drains the Paso Robles area and flows north into Monterey County. San Luis Obispo Creek passes through the county seat and reaches the Pacific Ocean beside Avila Beach. In the south, the Santa Maria River watershed spans parts of San Luis Obispo and Santa Barbara counties and includes the Cuyama and Sisquoc rivers.
Climate The county has a Mediterranean climate, with most rainfall occurring during the cooler part of the year. Conditions range from a cool, damp northern coast to a hot, dry interior, including the Cuyama Valley. The Garcia and Santa Lucia ranges intercept Pacific rain-bearing clouds and separate coastal marine air from the drier interior during much of summer. Summer fog is common along the coast, while inland valleys experience winter fog.
The San Luis Obispo area has a warm-summer Mediterranean climate (Csb) under the Köppen climate classification. For the 1991–2020 climate-normal period, the mean daily maximum temperature in July was at San Luis Obispo County Regional Airport and at Paso Robles Municipal Airport. The January mean daily minimum temperatures at the same stations were and , respectively.
Adjacent counties
National protected areas Carrizo Plain National Monument (part) Guadalupe-Nipomo Dunes National Wildlife Refuge Los Padres National Forest (part)
Marine protected areas
Cambria State Marine Conservation Area and State Marine Park Chumash Heritage National Marine Sanctuary Monterey Bay National Marine Sanctuary Morro Bay State Marine Recreational Management Area and Morro Bay State Marine Reserve Piedras Blancas State Marine Reserve and Marine Conservation Area Point Buchon State Marine Reserve and Marine Conservation Area White Rock (Cambria) State Marine Conservation Area
Demographics The 2020 census counted 282,424 residents. The U.S. Census Bureau estimated 282,367 residents on July 1, 2025. The California Department of Finance estimated the county's population at 279,242 on January 1, 2026.
2020 census
As of the 2020 census, the county had a population of 282,424. The median age was 41.4 years. 17.9% of residents were under the age of 18 and 21.7% of residents were 65 years of age or older. For every 100 females there were 98.7 males, and for every 100 females age 18 and over there were 97.2 males age 18 and over.
The racial makeup of the county was 70.2% White, 1.6% Black or African American, 1.1% American Indian and Alaska Native, 3.7% Asian, 0.1% Native Hawaiian and Pacific Islander, 9.7% from some other race, and 13.5% from two or more races. Hispanic or Latino residents of any race comprised 24.0% of the population.
80.9% of residents lived in urban areas, while 19.1% lived in rural areas.
There were 107,797 households in the county, of which 25.7% had children under the age of 18 living with them and 26.6% had a female householder with no spouse or partner present. About 26.6% of all households were made up of individuals and 13.2% had someone living alone who was 65 years of age or older.
There were 123,715 housing units, of which 12.9% were vacant. Among occupied housing units, 61.5% were owner-occupied and 38.5% were renter-occupied. The homeowner vacancy rate was 1.3% and the rental vacancy rate was 4.6%.
Racial and ethnic composition
+San Luis Obispo County, California – Racial and ethnic compositionRace / Ethnicity (NH = Non-Hispanic)Pop 1980Pop 1990Pop 2000Pop 2010 Pop 2020% 1980% 1990% 2000% 2010% 2020White alone (NH)132,809176,246187,840191,696183,46885.44%81.16%76.15%71.09%64.96%Black or African American alone (NH)2,6494,3254,7435,1284,3301.70%1.99%1.92%1.90%1.53%Native American or Alaska Native alone (NH)1,7861,6521,4901,3671,1361.15%0.76%0.60%0.51%0.40%Asian alone (NH)3,2045,7746,3428,10610,0012.06%2.66%2.57%3.01%3.54%Native Hawaiian or Pacific Islander alone (NH)x included in the Asian category in the 1980 Censusx included in the Asian category in the 1990 Census2273463400.09%0.13%0.09%0.13%0.12%Other race alone (NH)1952423657841,6140.13%0.11%0.15%0.29%0.57%Mixed race or Multiracial (NH)x The census first allowed respondents to identify with more than one race in 2000.x 5,4786,23713,614xx2.22%2.31%4.82%Hispanic or Latino (any race)14,79228,92340,19655,97367,9219.52%13.32%16.29%20.76%24.05%Total155,435217,162246,681269,637282,424 100.00%100.00%100.00%100.00%100.00%
2010 census The 2010 United States census reported that San Luis Obispo County had a population of 269,637. The racial makeup of San Luis Obispo County was 222,756 (82.6%) White, 5,550 (2.1%) African American, 2,536 (0.9%) Native American, 8,507 (3.2%) Asian (1.0% Filipino, 0.6% Chinese, 0.4% Japanese, 0.3% Indian, 0.3% Korean, 0.2% Vietnamese), 389 (0.1%) Pacific Islander, 19,786 (7.3%) from other races, and 10,113 (3.8%) from two or more races. Hispanic or Latino of any race were 55,973 persons (20.8%); 17.7% of San Luis Obispo County is Mexican, 0.3% Puerto Rican, and 0.2% Salvadoran.