Newark (/ˈnjuːərk/ NEW-ərk) is a city in Alameda County, California, United States. It was incorporated as a city in September 1955. Newark is an enclave, surrounded by the city of Fremont. The three cities of Newark, Fremont, and Union City make up the Tri-City Area. Newark's population was 47,529 at the 2020 census making it the third largest city in the US named Newark after Newark, New Jersey, and Newark, Ohio.

The western edge of the city is near the southern end of the San Francisco Bay. State Route 84 runs through the city, and continues as the Dumbarton Bridge to cross the San Francisco Bay to reach Menlo Park. Interstate 880 serves as the eastern boundary with Fremont.

According to the United States Census Bureau, the city has a total area of 13.9 square miles (36 km2), of which 13.9 square miles (36 km2) is land and 0.02 square miles (0.052 km2), comprising 0.17%, is water.

Newark was named after Newark Castle, Port Glasgow, in Scotland by J. Barr Robertson.

Before it was settled by Europeans, Newark was home to the Ohlone Native American Peoples. The first European settlement in the area was by the Spanish missionaries of Mission San José, whose territory covered much of the present-day cities of Newark, Fremont, and Union City. In 1878 land belonging to Washington Township of Alameda County was purchased by The Pacific Land Investment Company and subdivided to form the town of Newark.

In the early 1950s, the amalgamation of towns was increasing in Alameda County. In 1953, residents in the towns surrounding Newark were concerned about being annexed into the nearby city of Hayward, and began plans to incorporate as a single city, eventually becoming Fremont. Driven by their own concerns of being forced to amalgamate into this new city and the resulting changes in zoning, Newark was incorporated in September 1955, before the incorporation of Fremont would complete.

The 2010 United States Census reported that Newark had a population of 42,574. The population density was 3,063.2 inhabitants per square mile (1,182.7/km2). The racial makeup of Newark was 17,567 (41.3%) White, 2,002 (4.7%) Black, 279 (0.7%) Native American, 11,571 (27.2%) Asian, 621 (1.5%) Pacific Islander, 7,735 (18.2%) from other races, and 2,799 (6.6%) from two or more races. Hispanic or Latino of any race were 14,994 persons (35.2%).

The Census reported that 42,428 people (99.7% of the population) lived in households, 145 (0.3%) lived in non-institutionalized group quarters, and 0 (0%) were institutionalized.

There were 12,972 households, out of which 5,643 (43.5%) had children under the age of 18 living in them, 7,832 (60.4%) were opposite-sex married couples living together, 1,716 (13.2%) had a female householder with no husband present, 786 (6.1%) had a male householder with no wife present. There were 659 (5.1%) unmarried opposite-sex partnerships, and 93 (0.7%) same-sex married couples or partnerships. 1,942 households (15.0%) were made up of individuals, and 705 (5.4%) had someone living alone who was 65 years of age or older. The average household size was 3.27. There were 10,334 families (79.7% of all households); the average family size was 3.60.

The age distribution of the population shows 10,799 people (25.4%) under the age of 18, 3,824 people (9.0%) aged 18 to 24, 12,697 people (29.8%) aged 25 to 44, 10,727 people (25.2%) aged 45 to 64, and 4,526 people (10.6%) who were 65 years of age or older. The median age was 35.4 years. For every 100 females, there were 99.3 males. For every 100 females age 18 and over, there were 96.8 males.

There were 13,414 housing units at an average density of 965.2 per square mile (372.7/km2), of which 12,972 were occupied, of which 8,942 (68.9%) were owner-occupied, and 4,030 (31.1%) were occupied by renters. The homeowner vacancy rate was 1.0%; the rental vacancy rate was 4.0%. 28,489 people (66.9% of the population) lived in owner-occupied housing units and 13,939 people (32.7%) lived in rental housing units.

As of the census of 2000, there were 42,471 people, 12,992 households, and 10,341 families residing in the city. The population density was 3,039.4 inhabitants per square mile (1,173.5/km2). There were 13,150 housing units at an average density of 941.1 per square mile (363.4/km2).

There were 12,992 households, out of which 40.2% had children under the age of 18 living with them, 62.2% were married couples living together, 11.6% had a female householder with no husband present, and 20.4% were non-families. 14.1% of all households were made up of individuals, and 4.2% had someone living alone who was 65 years of age or older. The average household size was 3.26 and the average family size was 3.59.

In the city, the age distribution of the population shows 27.3% under the age of 18, 9.5% from 18 to 24, 34.3% from 25 to 44, 21.2% from 45 to 64, and 7.8% who were 65 years of age or older. The median age was 33 years. For every 100 females, there were 101.4 males. For every 100 females age 18 and over, there were 99.2 males.

The median income for a household in the city was $69,350, and the median income for a family was $71,351 (these figures had risen to $78,367 and $81,652 respectively as of a 2007 estimate). Males had a median income of $46,061 versus $34,959 for females. The per capita income for the city was $23,641. About 4.2% of families and 5.5% of the population were below the poverty line, including 5.7% of those under age 18 and 6.9% of those age 65 or over.

In the state legislature, Newark is in the 10th Senate District, represented by Democrat Aisha Wahab, and in the 25th Assembly District, represented by Democrat Ash Kalra. Federally, Newark is in California's 17th congressional district, represented by Democrat Ro Khanna.

Newark's economy is at the edge of Silicon Valley and shares its economic pattern.

Cargill Salt, previously known as Leslie Salt, operates a large salt refinery in Newark, cleaning salt produced in salt evaporation ponds in the San Francisco Bay.

The city houses the NewPark Mall, a super-regional shopping center, with anchor stores Macy's and Burlington Coat Factory, and over 140 other retailers. A 140,000-square-foot (13,000 m2) addition at NewPark, including restaurants, entertainment and a multiplex movie theater with IMAX, opened in 2015.

The former Sun Microsystems site near I-880, State Route 84 and the Dumbarton Bridge, was purchased by BioMed Realty Trust and is now known as the Pacific Research Center.

In the early to mid-20th century, Newark's economy was based on manufacturing, including: Wedgewood stoves (1910s–1940s); A.O. Smith Corporation, followed by National Steel Corporation, glass-lined water heaters (1950s–1970s); Peterbilt trucks (1960s-1980s); and Trailmobile semi-trailers (1965–1975).

According to the city's June 2020 Comprehensive Annual Financial Report, the top employers in the city are:

The City of Newark has thirteen parks and sport play facilities, the George M. Silliman Community Activity and Family Aquatic Center (aka the Silliman Center). The Family Aquatic Center portion of the Silliman Center opened in the summer of 2004 and includes a 32,300-square-foot (3,000 m2) indoor swim facility specifically designed for recreation, fitness, and instruction programs for the entire family. The 11,350-square-foot (1,054 m2) Natatorium includes four separate pools, including a 45 ft × 75 ft (14 m × 23 m) Activity Pool; a 245' long Lazy River pool (with a pair of 20' tall, curving water slides); a 4-foot (1.2 m) deep, 4-lane, 25-yard (23 m) Lap Pool; and a 15-person warm-water spa.

Newark also houses a portion of the Don Edwards San Francisco Bay National Wildlife refuge along with the city of Fremont.

Newark also hosts a festival in honor of the city's founding. "Newark Days" is a four-day Festival/Celebration that takes place every September on the Macgregor Soccer fields (adjacent to the Community center on Cedar Blvd).

Newark lies near the intersection of I-880, State Route 84, and the Dumbarton Bridge.

Newark is served by AC Transit bus system. Surrounding Fremont is the access point for most transportation services, including Fremont and Union City BART stations, and ACE and Amtrak trains.

In 2007, the ever-changing plans for the Dumbarton Rail Corridor, which has been talked about in fits and starts since 1988, envisioned Caltrain building a station in Newark.

Newark is home to a new campus of Ohlone College, a member of the California Community Colleges system. Other nearby educational centers include the University of Phoenix, ITT Institute, DeVry University, and Unitek College.