Ventura County was created in 1873 when it split from Santa Barbara County, bringing a flurry of changes to the area. A courthouse and wharf were built in San Buenaventura, the first officially recognized town in 1866, before the county was formed. A bank and public library were opened, and the school system grew, with the first high school opening in 1890.
The region’s roots extend to the precolonial period, when Ventura County was inhabited by the Chumash people, who also settled much of Santa Barbara and San Luis Obispo counties 10,000 to 12,000 years ago. The Chumash were hunter-gatherers and fishermen, and they traded with the Mojave, Yokuts and Tongva Indians. The Chumash were known for their rock paintings and basketry.
In 1542, a Spanish expedition led by Juan Rodriguez Cabrillo brought the first Europeans to the area. Occupation by Spain began in 1769. Mission San Buenaventura was founded in 1782 by Father Junipero Serra, named for Saint Bonaventure, one of the early intellectual founders of the Franciscan Order. The town that grew up around the mission retains its original name of San Buenaventura.
After Mexico gained its independence from Spain in 1821, the California territory became part of Mexico. By the 1930s, Mission San Buenaventura was in decline. After the Mexican-American War, the California territory was formally transferred to the United States in 1848. The next year, a constitution was adopted for the California territory. The new legislature met and divided the pending state into 27 counties. At the time, the area that would become Ventura County was the southern part of Santa Barbara County.
Other towns were starting to form in the county. A plan for Hueneme (later Port Hueneme) was recorded in 1874, and Santa Paula’s plan was recorded in 1875. The community of Nordhoff (later renamed Ojai) was started in 1874. Bardsdale, Fillmore, Piru and Montalvo were established in 1887. In 1892, Simi (later Simi Valley), Somis, Saticoy and Moorpark were established. Oxnard was a late-comer, established in 1898.
The Southern Pacific Railroad laid tracks through San Buenaventura in 1887. For convenience in printing its timetables, Southern Pacific shortened San Buenaventura to Ventura. The post office soon followed suit. While the city’s official name is San Buenaventura, it is commonly known as Ventura.
The rail line to Northern California originally went through Saugus, Fillmore and Santa Paula, providing a boom for those communities. In 1905, Tunnel No. 26 was completed between Chatsworth and Corriganville near Simi Valley, shortening the rail route. The tunnel joined the railroad spur coming in the other direction from Montalvo through Camarillo, Moorpark and Simi Valley, creating the main line used today. One stop along the way was at a sugar beet processing factory that bore the name of its absentee owners, the Oxnard brothers. A community of farm and factory workers grew near the train stop. That community eventually became the largest city in Ventura County — Oxnard — with a population of 207,254, according to 2015 census estimates.
Oil has been known in Ventura County since the Chumash people used tar from natural seeps as a sealant and waterproofing for baskets and canoes. However, in 1913, oil exploration began in earnest, with Ralph Lloyd obtaining the financial support of veteran oil man Joseph B. Dabney. Their first well, named “Lloyd No. 1,” was drilled in 1914. The well struck oil but was destroyed when it went wild. Other wells met a similar fate, until 1916, when a deal was struck with the Shell Oil Co.
As the nation’s demand for oil grew, Ventura County became a major oil producer. Ventura County experienced tremendous population growth during the 1920s primarily because of the discovery of the largest oil field in the county, the Ventura Avenue Oil Field, in 1919.
Meanwhile, the town of Santa Paula underwent significant changes with the discovery of the South Mountain Oil Field in 1916. Until then, agriculture was the only large industry, but the discovery of oil at South Mountain created a boom that lasted 10 years. More oil fields came online in the 1920s and 1930s, with the Rincon field, the second-largest, in 1927, and the adjacent San Miguelito in 1931.
Ventura County can be separated into two major parts: East County and West County. East County consists of all cities east of the Conejo Grade, a 7 percent grade incline of the Ventura Freeway linking Thousand Oaks and cities of the Conejo Valley with Camarillo and cities on the Oxnard Plain.
West County, which is everything west of the Conejo Grade, consists of cities such as Camarillo, Oxnard, Somis, Point Mugu, Port Hueneme, Ventura, Ojai, Santa Paula and Fillmore. West County consists of some of the first developed cities in the county. The largest beach communities are in West County on the coastline of the Channel Islands Harbor.