Walnut Creek is a city in Contra Costa County, California, United States, located in the East Bay region of the San Francisco Bay Area, about 16 miles (26 kilometers) east of the city of Oakland. Walnut Creek has a total population of 70,127 per the 2020 census, is located at the junction of the highways from Sacramento and San Jose (I-680) and San Francisco/Oakland (SR-24), and is accessible by BART. The city shares its borders with Clayton, Lafayette, Alamo, Pleasant Hill, and Concord.

There are three bands of Bay Miwok Native Americans associated with the area of Walnut Creek (the stream for which the city is named): the Saclan, whose territory extended through the hills east of present-day cities of Oakland, Rossmoor, Lafayette, Moraga and Walnut Creek; the Volvon (also spelled Bolbon, Wolwon or Zuicun), who were near Mt. Diablo; and the Tactan, located on the San Ramon Creek in present-day Danville and Walnut Creek.

The city of Walnut Creek has developed within the earlier area of four extensive Mexican land grants. One of these land grants – measuring 18,000 acres (73 km2) – belonged to Juana Sanchez de Pacheco. The grant was called Rancho Arroyo de Las Nueces y Bolbones, named after the principal waterway, Arroyo de las Nueces (Walnut Creek in English), and for the local group of Volvon indigenous Americans (also known as Bolbones in Spanish). The Arroyo de las Nueces was named for the local species of walnut tree, the California Walnut. The two grandsons of Sanchez de Pacheco inherited the thousands of acres of land. One, Ygnacio Sibrian, built the first roofed home in the valley in about 1850.

As settlers from the United States arrived following US annexation of California after victory in the Mexican–American War, a small settlement called "The Corners" emerged. It was named for the junction where roads met from the settlements of Pacheco and Lafayette. The intersection of Mt. Diablo Boulevard and North Main Street is now at this site. The first town settler was William Slusher, who built a dwelling on the bank of Walnut Creek, first called "Nuts Creek" by Americans in 1849. In 1855, Milo Hough of Lafayette built the hotel named "Walnut Creek House" in The Corners. A blacksmith shop and a store were soon established by settlers. In 1850 Hiram Penniman laid out the town site and realigned Main Street to what it is today. (Penniman also developed Shadelands Ranch.)

In December 1862 a United States Post Office was established here, named "Walnut Creek". Pioneer Homer Shuey platted the downtown street patterns in 1871–1872 on a portion of one of his family's large cattle ranches. These streets have been maintained to the present.

The arrival of Southern Pacific Railroad service in 1891 stimulated development of Walnut Creek. On October 21, 1914, the town and the surrounding area were incorporated as the 8th city in Contra Costa County. A branch line of the Southern Pacific ran through Walnut Creek until the late 1970s. Portions were adapted by East Bay Regional Park District for the Iron Horse Trail, which is used by walkers, runners and bikers. The mainline of the Sacramento Northern Railway passed through Walnut Creek. Both railroads had stations here. Today, the Yellow Line of the Bay Area Rapid Transit (BART) serves Walnut Creek with a station adjacent to Highway 680.

With the 1951 opening of the downtown Broadway Shopping Center (now Broadway Plaza), Contra Costa County's first major retail center, the city took off in a new direction. In the postwar period of suburban development, its population more than quadrupled – from 2,460 in 1950 to 9,903 in 1960. Growth has accelerated since the late 20th century, with a population just over 70,000 according to the latest census.

Walnut Creek is located at 37°54′23″N 122°03′54″W / 37.90639°N 122.06500°W / 37.90639; -122.06500. Portions lie in both the San Ramon Valley and the Ygnacio Valley below the western slopes of Mount Diablo. According to the United States Census Bureau, the city has a total area of 19.8 sq mi (51.2 km2), 0.06 percent of which is water. Walnut Creek – the actual waterway that runs through the town – has been routed underneath downtown through a series of tunnels. These start at the southwest end of Macy's and end just southwest of Bar Camino Restaurant.

Walnut Creek consists of a bustling, upscale downtown with established neighborhoods in its surrounding areas. Neighborhoods range in affordability and feel, with some being exceptionally charming and tight-knit (e.g., Parkmead) while others are more rural and forested with homes on generous lots (e.g., Tice Valley). Not all neighborhoods are incorporated; there are many unincorporated areas that are serviced by Contra Costa County. A non-exhaustive list of neighborhoods in Walnut Creek include:

Depending on the neighborhood, homes can be assigned to schools in Lafayette, San Ramon Valley, Walnut Creek, or Mt. Diablo Unified School District.

Walnut Creek owns more open space per capita than any other community in the state of California. In 1974, Walnut Creek voters approved a $6.7 million bond measure to acquire and protect open space: the city purchased 1,800 acres (730 ha) of undeveloped hillsides, ridge lines, and park sites. Walnut Creek owns parts of Lime Ridge Open Space, Acalanes Ridge Open Space, Shell Ridge Open Space, and Sugarloaf Open Space.

The East Bay Regional Park District operates Diablo Foothills Regional Park and Castle Rock Regional Recreation Area, both of which are located in Walnut Creek.

Walnut Creek's warm summer Mediterranean climate (Köppen climate classification Csb) is typical of California's interior valleys. In summer, high pressure results in almost unbroken sunshine and virtually no precipitation. Days start out cool but quickly warm up, with high temperatures normally in the 80s Fahrenheit (27 to 32 Â°C). Temperatures of 100 Â°F (38 Â°C) or hotter occur numerous times during heatwaves, however. In the winter, the jet stream moves far enough south so that Pacific storms can reach Walnut Creek, bringing much-needed rain – average annual rainfall approximates 26 inches (660 mm), with slight variations occurring in microclimates based on elevation and topography. During particularly cold storms, snow falls on the peak of nearby Mount Diablo, but snow in the valley floor is very rare. There are numerous clear, mild days in winter, often with morning frost. The climate allows for the successful cultivation of many plants and crops, being warm enough for citrus yet cold enough for apples. The Ruth Bancroft Garden is a renowned botanical garden that showcases the diversity of plants that can be successfully grown.

The city has two Bay Area Rapid Transit (BART) stations – Walnut Creek and Pleasant Hill (in the unincorporated area known as Contra Costa Centre Transit Village) – both served by the Yellow Line.

Central Contra Costa Transit Authority (County Connection/CCCTA) provides bus service throughout Walnut Creek and Contra Costa County at a modest cost. County Connection also operates three free weekday shuttles within city limits: the Downtown Trolley/Route 4 loops from Walnut Creek BART to Broadway Plaza; Route 5 runs from Walnut Creek BART to Creekside; and Route 7, which runs from Pleasant Hill BART to Shadelands Business Park.

Walnut Creek is transected by the Iron Horse Trail (running north–south) through its downtown, as well as the Contra Costa Canal Trail (running east–west) at the north end of the city. Both these trails, in addition to city bike lanes, make bicycle transportation feasible both for recreation and as an alternative commute.

The 2010 United States Census reported that Walnut Creek had a population of 64,173. The population density was 3,246.2 inhabitants per square mile (1,253.4/km2). The racial makeup of Walnut Creek was 50,487 (78.7 percent) White, 1,035 (1.6 percent) African American, 155 (0.2 percent) Native American, 8,027 (12.5 percent) Asian, 125 (0.2 percent) Pacific Islander, 1,624 (2.5 percent) from other races, and 2,720 (4.2 percent) from two or more races. Hispanic or Latino of any race were 5,540 persons (8.6 percent).

The Census reported that 63,171 people (98.4 percent of the population) lived in households, 176 (0.3 percent) lived in non-institutionalized group quarters, and 826 (1.3 percent) were institutionalized.

There were 30,443 households, out of which 6,363 (20.9 percent) had children under the age of 18 living in them, 13,305 (43.7 percent) were opposite-sex married couples living together, 2,071 (6.8 percent) had a female householder with no husband present, 844 (2.8 percent) had a male householder with no wife present. There were 1,286 (4.2 percent) unmarried opposite-sex partnerships, and 298 (1.0 percent) same-sex married couples or partnerships. 11,884 households (39.0 percent) were made up of individuals, and 6,424 (21.1 percent) had someone living alone who was 65 years of age or older. The average household size was 2.08. There were 16,220 families (53.3 percent of all households); the average family size was 2.79.

The population was spread out, with 10,719 people (16.7 percent) under the age of 18, 3,599 people (5.6 percent) aged 18 to 24, 15,137 people (23.6 percent) aged 25 to 44, 17,653 people (27.5 percent) aged 45 to 64, and 17,065 people (26.6 percent) who were 65 years of age or older. The median age was 47.9 years. For every 100 females, there were 86.4 males. For every 100 females age 18 and over, there were 83.0 males.

There were 32,681 housing units at an average density of 1,653.2 units per square mile (638.3 units/km2), of which 20,262 (66.6 percent) were owner-occupied, and 10,181 (33.4 percent) were occupied by renters. The homeowner vacancy rate was 2.4 percent; the rental vacancy rate was 6.7 percent. 43,079 people (67.1 percent of the population) lived in owner-occupied housing units and 20,092 people (31.3 percent) lived in rental housing units.

City Council members are elected at-large to staggered, four-year terms, in elections held in even-numbered years.

As of 2022, the current elected representatives are Matt Francois (Mayor), Cindy Silva (Mayor Pro Tem), Loella Haskew, Cindy Darling and Kevin Wilk (Council members).

On the Contra Costa County Board of Supervisors, Walnut Creek is split between Supervisorial District 2 and Supervisorial District 4, represented by Candace Andersen and Karen Mitchoff, respectively.

In the California State Legislature, Walnut Creek is split between the 14th Assembly District, represented by Democrat Buffy Wicks and the 16th Assembly District, represented by Democrat Rebecca Bauer-Kahan and in the 7th Senate District, represented by Democrat Jesse Arreguín.

In the United States House of Representatives, Walnut Creek is located in California's 10th congressional district, represented by Mark DeSaulnier (D–Concord).

According to the California Secretary of State, as of February 10, 2019, Walnut Creek has 46,149 registered voters. Of those, 21,391 (46.4%) are registered Democrats, 10,708 (23.2%) are registered Republicans, and 12,147 (26.3%) have declined to state a political party.

Walnut Creek residents attend schools in five public school districts. The Walnut Creek School District (K–8) has five elementary schools, one magnet school (K–8), and one middle school in the city. Some residents are served by schools from the Mount Diablo Unified School District (K–12), the Acalanes Union High School District (9–12), the San Ramon Valley Unified School District (K–12), and the Lafayette School District (K–8). The Walnut Creek and Lafayette districts feed into Acalanes Union HSD.

The following public schools are within the city limits of Walnut Creek:

Walnut Creek is home to several private schools, including:

The Walnut Creek Library and the Ygnacio Valley Library of the Contra Costa County Library are located in Walnut Creek. The Ygnacio Valley Branch, which opened in 1975, is also known as the Thurman G. Casey Memorial Library. Fundraising and other support is provided by the Walnut Creek Library Foundation.

On February 26, 2008, the city demolished the Walnut Creek Library, that was built in 1961 at the southern end of Civic Park. Mayor Gwen Regalia hosted a groundbreaking on the same site for the new library on May 19, 2008. The new library, designed by Group 4 Architecture, Research + Planning, Inc., has 42,000 square feet (3,900 m2) and an underground parking garage. Construction was completed in 2010 and the library was officially opened on July 17, 2010.

Companies based in Walnut Creek include Central Garden & Pet (makers of the AvoDerm, Amdro, Kaytee brands, among others), American Reprographics Company, CSE Insurance Group, Maximum Games, and the PMI Group.

Walnut Creek is served by the daily newspaper, The East Bay Times (formerly The Contra Costa Times). The paper was originally run and owned by the Lesher family. Since the death of Dean Lesher in 1993, the paper has had several owners. The Times, as it is known, has a section called "The Walnut Creek Journal."

Walnut Creek TV (WCTV) is the city's government-access television channel, covering local government and community events. WCTV is available in Walnut Creek on Comcast channel 28 (channel 26 in Rossmoor), Astound channel 29, AT&T U-verse channel 99 under the menu option "Walnut Creek Television", and on YouTube. Claycord.com is the widely read independent news and talk blog serving the greater Walnut Creek metropolitan area.