Anthropologist John P. Harrington in about 1900 wrote what he was told by the local Chumash People:
This story may be related to the lore about the Paleo-Indians, who are believed by some to be the distant ancestors of the Chumash. Mammoth fossils were unearthed in Newbury Park in 1961 and later in 1971, and are on display at the Stagecoach Inn Museum. The Newbury Park area is believed to have been inhabited by people of the Chumash culture for at least the past 6,000, 7,000, 8,000, or perhaps 10,000 years. Newbury Park has been home of three Chumash villages: Satwiwa by the southern edge of town, as well as two villages that were located by today’s Ventu Park Road. These villages were settled 2,000 years ago, and had a population of 100–200 inhabitants in each village. In addition to those three, a large Chumash village was located just north of Arroyo Conejo Open Space by Wildwood Regional Park. Other nearby villages include Lalimanux (Lalimanuc or Lalimanuh) at the base of the Conejo Grade by westernmost Newbury Park, as well as Kayɨwɨš or Kayiwish (Kawyis) (CA-Ven-243) also by the Conejo Grade. This region contains numerous pictographs.
Newbury Park contains many ancient burial sites, most near the Santa Monica Mountains in the southern portion of the community. Many burial items have been discovered in the area, most notably by Rancho Sierra Vista in southern Newbury Park. Satwiwa, which is Chumash for “the bluffs”, was the name of a nearby village by the Big Sycamore Canyon. The canyon was a popular trading route for the Chumash- and Tongva people, connecting the Conejo Valley to Mugu Lagoon through the Santa Monica Mountains. Unlike Satwiwa, which is now protected as a part of the Santa Monica Mountains National Recreation Area, the two other Chumash villages once located within Newbury Park are located on private lands by Ventu Park Road. These are known as CA-Ven-65, CA-Ven-261, and CA-Ven-260 near the Fieldhouse in Newbury Park. At CA-Ven-261 is an ancient Chumash burial site as suggested by a village of long duration.
The Ventureño Chumash initially settled in the west end of the Santa Monica Mountains because of the abundant food supply. Roots, berries, seeds, bulbs, acorns and walnuts were plentiful in the region, and a variety of wildlife including birds, deer and squirrels made for good hunting. Shellfish and fish were transported from the nearby Mugu Lagoon across the Santa Monicas. Here they also discovered an abundance of jackrabbits and other rabbit species, which were hunted widely for fur and meat. At one point, the Chumash here gathered a group of 27 men and killed hundreds of rabbits during a rabbit round-up, which was a significant event of late summers in the Conejo Valley. Along with Rancho Sierra Vista, various Chumash artifacts from these older settlements, along with petroglyphs, have been found along the Arroyo Conejo, particularly in the Santa Monica Mountains.
The Satwiwa Native American Indian Culture Center and the Stagecoach Inn Museum in Newbury Park have displays built around some of these finds, as does the Chumash Indian Museum in Thousand Oaks. In partnership with Friends of Satwiwa, the National Park Service began talks of establishing the current Satwiwa Native American Indian Culture Center and Natural Area in 1978. Boney Mountain in southern Newbury Park is now a sacred site for the Chumash, and nearby Satwiwa is frequently used by the Chumash Barbareño-Ventureño Band of Mission Indians for private events such as traditional dances and sacred ceremonies.
When the Europeans first arrived in the Conejo Valley, they pressed plow to furrow and fields to barley and wheat.
Newbury Park is named after its founder, Egbert Starr Newbury, who owned thousands of acres of land in the Conejo Valley and later became the first postmaster. E.S. Newbury, Howard Mills, and John Edwards were among the first to buy former Rancho El Conejo land in the early 1870s. El Rancho Conejo was an area which today encompasses most of the Conejo Valley and was named for its many rabbits. Its name derives from a Spanish land grant in California, encouraged by the Spanish- and Mexican governments.
Newbury and his wife Fannie moved to California from Michigan of health reasons in 1871. He later became the first postmaster in the Conejo Valley in 1875. The post office was near their house which was located at the current location of the Thousand Oaks Civic Arts Plaza. E.S. Newbury purchased 2,200 acres of land in 1874, which stretched from today’s old town Thousand Oaks and into Hidden Valley in southern Newbury Park.
In the 1870s, Egbert S. Newbury and his wife Fannie moved full-time to their ranch in Conejo Valley which they named “Newbury Park” because the land looked so much like a park community. It consisted of his house, barn, and a guest house for visitors to “enjoy the healthful climate”, according to E.S. Newbury. The area was remote and only five families lived in the Conejo Valley at the time, all on large ranch lands. The ranches were miles apart and there were no grocery stores, medical facilities, schools, or churches in the valley. Newbury had acres of wheat and owned thousands of sheep. The weather had a great impact on his health, and he wrote to his sister Kittie in Michigan on November 23, 1874:
«take wings and come to Conejo and enjoy our warm bright days all winter… be outdoors instead of confined indoors… I am out all the time and our drives now are just lovely with the country all turning green. The birds stay around our house in flocks all the time… Our roads to the ranch are splendid and they lie through beautiful canyons and large groves of live and white oak and sycamore, then into an open valley with slopes and surrounding hills covered with evergreen oaks…».
As a result of the increasing interest in the developing Conejo Valley, Newbury functioned as a public relations representative for the Conejo Valley. On December 25, 1875, E.S. Newbury wrote in the largest newspaper in Ventura County at the time, the Ventura Signal, the following words about Newbury Park:
«Next to Ojai and Santa Ana ranchos, the Conejo mountain valley has the best reputation as a health resort. It is well fifteen miles from Port Hueneme. The soil is immensely fertile, producing large crops of wheat and other grain…».
Before Newbury Park existed, the Grand Union Hotel provided a stopover for travelers that dates back to 1876. The hotel was operated as a health- and pleasure resort, and provided a rest stop for stagecoach passengers and a gathering place for residents in Newbury Park.
The Conejo Valley pioneers were living in rugged individualism, where travelers had to make their journey over the Conejo Grade or Norwegian Grade to reach Camarillo where they could buy groceries. Newbury Park was an older settlement than Thousand Oaks, where people had settled wedged between Borchard lands on the south and Friedrich land on the north. The residents of the Conejo Valley had to travel to Oxnard for high school, burials or for marriages.
As inhabitants of the valley had to travel to San Buenaventura (Ventura, CA) to get their mail, E.S. Newbury took the initiative to establish a local post office and applied to Washington, D.C. On July 16, 1875, the Newbury Park Post Office was established with E.S. Newbury as its first postmaster.
The Conejo School District was established in March 1877. At the time, the population was 126 in the Conejo Valley. E.S. Newbury and other residents of the Conejo Valley were unprepared for the 1876–78 drought. There were only six inches of rain in 30 months. The drought devastated Newbury Park and the valley. With no rain, the crops died and natural grasses as well, which were food for the ranchers’ sheep. Egbert went bankrupt and decided to move with his family in 1877, and rode with his wagon and family back to Michigan where he ultimately settled in Detroit. On September 28, 1878, the land Egbert once called “Newbury Park” was sold at a sheriff’s sale. The post office remained its original name, despite having moved from its original destination, which is why Newbury Park has its name today.
Newbury Park was a more established and older community than Thousand Oaks at the beginning of the 20th century.
In the early 20th century, Newbury Park had a few ranches and stores, wedged between Borchard lands to the south and Friedrich land on the north. During the 1940s, Ventu Park behind Newbury Park’s main street became a 500-acre real estate development. Lots sold to movie stars and others seeking a rustic retreat. One of the male members of the New York Rothschilds built a large home by Ventu Park and lived in relative seclusion here in the 1940s.
Prior to the 1960s, Newbury Park was never incorporated as its own city or municipality, it was unincorporated areas of Ventura County with little development. During the 1950s there were speculations persisting that Ventura County officials refused to allow Newbury Park to expand because of a feud with the would-be developers. Between 1950 and 1970, the Conejo Valley experienced a population boom, and increased its population from 3,000 to 30,000.
Many Newbury Park residents did not want to be part of Thousand Oaks, and many residents fought to stop the incorporation in fear of losing the Newbury Park identity. Newbury Park had made failed attempts at creating its own municipality in the early 1960s, not only to create its own city, but to also remain independent of Thousand Oaks. A 1963 attempt at a cityhood election failed when the Janss’s Rancho Conejo Industrial Park and the Talley Corporation refused to join the efforts. Activist Reba Hays Jeffries of the Stagecoach Inn had a different explanation for interviewers when addressing why efforts at an independent municipality failed. She claimed the cityhood supporters were required to collect signatures from owners who represented 29% of the land area in Newbury Park. As the efforts collected signatures from 29% of registered voters, and not Newbury Park landowners, the petition never appeared on the ballot. Reba M.H. Jeffries was one of several opponents to the idea of annexation when it was first proposed in 1967. Jeffries feared for the identity of Newbury Park and was quoted in an interview saying: “It’s a shame that the Thousand Oaks personality is overpowering to the extent that Newbury Park is losing its large ranches and freedom.” Jeffries was also opposed to the proposition to demolish the Stagecoach Inn in 1964, and fought to keep the Newbury Park Post Office in town.
The City of Thousand Oaks was formally established on September 29, 1964, and throughout the late 1960s and throughout the 1970s, most Newbury Park land was annexed by the City of Thousand Oaks. The annexed area was formerly controlled by Ventura County, but as of 2016, all but Casa Conejo and Ventu Park is within Thousand Oaks city limits. Together with Thousand Oaks, Newbury Park was part of a master planned community by the Janss Investment Company.
Newbury Park has had an increasing population due to the presence of biotechnology firms and technology corporations, such as Amgen (world headquarters) and Baxter, and other high-technology corporations.
President George W. Bush visited the Newbury Park High School and the Satwiwa Native American Indian Culture Center in 2003.
The community contains two major new residential areas, Rancho Conejo Village (built on the site of the former Rancho Conejo Airport, where portions of the film It’s a Mad, Mad, Mad, Mad World were filmed) and Dos Vientos Ranch. The first planned community in Newbury Park was Casa Conejo, located in a roughly square-shaped unincorporated area.