Pittsburg (formerly Black Diamond, New York Landing and New York of the Pacific) is a city in Contra Costa County, California, United States. It is an industrial suburb located on the southern shore of the Suisun Bay in the East Bay region of the San Francisco Bay Area, and is part of the Sacramento–San Joaquin River Delta area, the Eastern Contra Costa County area, and the San Francisco Bay Area. The population was 76,416 at the 2020 United States Census.

Originally settled in 1839 as “Rancho Los Medanos”, the area of almost 10,000 acres was issued to Californios Jose Antonio Mesa and his brother Jose Miguel under a Mexican Land Grant by then Governor Juan Bautista Alvarado, one of the final land grants issued prior to the formation of California as a state.

In 1849, during the California Gold Rush, Colonel Jonathan D. Stevenson (from New York) bought the Rancho Los Medanos land grant for speculation, and laid out a town he called "New York of the Pacific". General William Tecumseh Sherman laid out the first network of streets on the west side of town. The area was the midway stopping point for schooners traveling from San Francisco to the gold country further inland. Fishing, farming, and cattle raising for the hide and tallow industry were the major economic activities during this time.

In 1859, with the discovery of coal in the nearby town of Nortonville, the place became a port for coal. The Black Diamond Coal Mining Company commenced operations, building the Black Diamond Coal Mining Railroad to Nortonville. Steam powered engines moved coal cars down the tracks along present day Railroad Avenue to the waterfront docks that came to be called "Black Diamond Landing." The boom ended in 1885, and the company moved to Washington state to work a new claim.

In the 1870s, commercial fishing took hold and the Black Diamond Cannery was established at the foot of Los Medanos St. By 1882, a network of ten canneries was formed along the Sacramento Delta. An industry was born with fishermen, packing plants, boat builders and the like dominating the local waterfront for the next 80 years. The town boasted the largest Delta fishing community in the state, made up primarily of Sicilian immigrants, the families of which have remained in the area for generations. In 1957, the State of California closed down the Sacramento Delta to commercial fishing, ending the area's industry.

In 1900, C.A. Hooper purchased the land grant and gave birth to many manufacturing ventures, beginning in 1903 with the creation of the Industrial Center of the West. Hooper secured additional capitalization and provided property for the Columbia Steel Company, which, in 1910, opened its California steel plant in Pittsburg with one foundry and a crew of 60 employees. It made steel castings for the dredging, lumber and shipping industries.

In 1903 the town was incorporated, and by a vote of the citizenry, was renamed "Black Diamond", after the mining firm. Because of the industrial potential of the site, a name change to Pittsburg was proposed in 1909. On February 11, 1911, the city officials changed the town's name to "Pittsburg", honoring Pittsburgh, Pennsylvania, as the two cities shared a common steel and mining industrial heritage. This rechristening came at a time when the name of Pittsburgh, Pennsylvania was more commonly spelled without the "h". In 1918 the shipyard of the Pacific Coast Shipbuilding Company was built in neighboring Bay Point, the associated company town of Clyde, California alongside it, but as soon as the World War I shipbuilding boom was over, the yard was closed in 1921.

In 1930, Columbia Steel became a subsidiary of U.S. Steel. At that point the company had expanded into Utah and was worth $40,000,000. The Pittsburg plant continued to grow until the early 1950s, reaching a peak staff of 5,200 employees when the markets for its products crashed. The parent company (by 1986, renamed as USS Company) had merged with Korean Pohang Iron and Steel Company. Together they invested $450 million turning the Pittsburg plant into a modern flat-products mill, renamed as USS-Posco. As of 1999, the facility employed 970 workers and shipped over 1.6 million U.S. tons per year of steel to over 175 customers in the Western U. S., Mexico, Canada and the Pacific Rim.

The original town site fronts on the Sacramento/San Joaquin River Delta, reflecting its origins as a deep water channel river port (As of January 1, 2007, state legislation [Assembly Bill 2324] enabled the city to manage its own riverfront for commercial development and subsequent port operations). Since the early 1900s, the city has grown inland to the south, then spread east and west along State Route 4, now a freeway carrying resident commuters to jobs in the San Francisco Bay-Oakland Region. In the process, the former town of Cornwall, California was absorbed. As of the 2000 census, the city had a total population of 56,769.

Camp Stoneman was built in 1942, and was a major staging area for the United States Army during World War II and the Korean War until 1954.

The first post office opened in 1868 as Black Diamond, and changed its name with the town's in 1911.

Pittsburg shares a border with the unincorporated community of Bay Point, California to the west, the city of Concord, California to the southwest and Antioch, California to the east. The Suisun Bay is directly north of the city and connects the San Francisco Bay to the Sacramento and San Joaquin rivers.

Pittsburg experiences a hot summer Mediterranean climate (Köppen climate classification Csa) bordering on the Semi-arid climate because of the Mt. Diablo rain shadow in East Contra Costa County.

The 2020 United States Census reported that Pittsburg had a population of 77,572. The population density was 4,323.2 inhabitants per square mile (1,669.2/km2). The racial makeup of Pittsburg was 23,106 (27.3%) White, 11,187 (15.2%) African American, 517 (1.2%) Native American and Alaska Native alone, 13,808 (17.8%) Asian, 645 (1.0%) Pacific Islander, 13,270 (7.2%) from other races, and 4,648 (14.2%) from two or more races. Hispanic or Latino of any race were 26,841 persons (43.2%).

The 2010 United States Census reported that Pittsburg had a population of 63,264. The population density was 3,302.8 inhabitants per square mile (1,275.2/km2). The racial makeup of Pittsburg was 23,106 (36.5%) White, 11,187 (17.7%) African American, 517 (0.8%) Native American, 9,891 (15.6%) Asian (9.9% Filipino, 2.0% Indian, 1.2% Chinese, 1.1% Vietnamese, 0.2% Korean, 0.2% Japanese, 1.1% Other), 645 (1.0%) Pacific Islander, 13,270 (21.0%) from other races, and 4,648 (7.3%) from two or more races. Hispanic or Latino of any race were 26,841 persons (42.4%).

The Census reported that 62,973 people (99.5% of the population) lived in households, 153 (0.2%) lived in non-institutionalized group quarters, and 138 (0.2%) were institutionalized.

There were 19,527 households, out of which 8,837 (45.3%) had children under the age of 18 living in them, 9,833 (50.4%) were opposite-sex married couples living together, 3,583 (18.3%) had a female householder with no husband present, 1,420 (7.3%) had a male householder with no wife present. There were 1,432 (7.3%) unmarried opposite-sex partnerships, and 194 (1.0%) same-sex married couples or partnerships. 3,446 households (17.6%) were made up of individuals, and 1,067 (5.5%) had someone living alone who was 65 years of age or older. The average household size was 3.22. There were 14,836 families (76.0% of all households); the average family size was 3.64.

The population was spread out, with 17,385 people (27.5%) under the age of 18, 6,823 people (10.8%) aged 18 to 24, 18,319 people (29.0%) aged 25 to 44, 15,298 people (24.2%) aged 45 to 64, and 5,439 people (8.6%) who were 65 years of age or older. The median age was 32.5 years. For every 100 females, there were 94.9 males. For every 100 females age 18 and over, there were 92.4 males.

There were 21,126 housing units at an average density of 1,102.9 units per square mile (425.8 units/km2), of which 19,527 were occupied, of which 11,490 (58.8%) were owner-occupied, and 8,037 (41.2%) were occupied by renters. The homeowner vacancy rate was 3.8%; the rental vacancy rate was 6.8%. 37,078 people (58.6% of the population) lived in owner-occupied housing units and 25,895 people (40.9%) lived in rental housing units.

As of the census of 2000, there were 56,769 people, 17,741 households, and 13,483 families residing in the city. The population density was 3,639.0/sq mi (1,405.0/km2). There were 18,300 housing units at an average density of 1,173.1 units per square mile (452.9 units/km2). The racial makeup of the city was 36.53% White, 25.89% Black or African American, 0.75% Native American, 12.65% Asian, 0.86% Pacific Islander, 16.11% from other races, and 7.22% from two or more races. 32.21% of the population were Hispanic or Latino of any race.

There were 17,741 households, out of which 42.2% had children under the age of 18 living with them, 52.5% were married couples living together, 17.2% had a female householder with no husband present, and 24.0% were non-families. 18.0% of all households were made up of individuals, and 5.8% had someone living alone who was 65 years of age or older. The average household size was 3.17 and the average family size was 3.59.

In the city, the population was spread out, with 30.8% under the age of 18, 10.4% from 18 to 24, 31.2% from 25 to 44, 19.4% from 45 to 64, and 8.2% who were 65 years of age or older. The median age was 31 years. For every 100 females, there were 96.6 males. For every 100 females age 18 and over, there were 94.1 males.

The median income for a household in the city was $50,557, and the median income for a family was $54,472. Males had a median income of $39,111 versus $31,396 for females. The per capita income for the city was $18,241. About 8.7% of families and 11.5% of the population were below the poverty line, including 14.1% of those under age 18 and 7.6% of those age 65 or over.

Coal mining and industry have been part of the economy since the late 1800s. USS-POSCO Industries (a joint venture between US Steel and POSCO of South Korea) and Corteva maintaining plants in Pittsburg.

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

The Pittsburg Historical Museum, established in 1961, has been situated in the historic former Pittsburg Post Dispatch building since 2003.

The California Theatre, opened in 1920, began as a venue for live vaudeville performances and silent films. During its heyday, notable performers included Flash Gordon and cowboy heroes Ray “Crash” Corrigan, Tim Holt, Tex Ritter and Fred Scott. The California Theatre closed in 1954 and began to deteriorate, prompting a $7.6 million renovation in 2008 and an additional $2 million restoration in 2022. Today, the auditorium features a 981-seat capacity, beaux-artes style ceiling decoration, and a grand balcony.

Pittsburg hosts one of the many Contra Costa County Libraries.

The Pittsburg Diamonds, was an independent professional baseball team, in the Pacific Association of Professional Baseball Clubs from 2014 to 2019. The team played its home games in City Park Field #1 until going on hiatus for 2019 and 2020. The Pacific Association has since folded, leaving Pittsburg without independent baseball.

According to the California Secretary of State, as of February 10, 2019, Pittsburg has 33,751 registered voters. Of those, 18,644 (55.2%) are registered Democrats, 3,817 (11.3%) are registered Republicans, and 9,888 (29.3%) have declined to state a political party.

Pittsburg is home to Los Medanos College, a two-year community college that is part of the Contra Costa Community College District. The college's name is derived from that of Rancho Los Medanos, one of the land grants made by the Mexican Government during its sovereignty over California from 1821 to 1846; Los Medanos, loosely translated from Spanish, means The Sand Dunes. Construction on Los Medanos College was completed in 1974.

Schools located within Pittsburg are administered by the Pittsburg Unified School District, and include:

The city has two BART stations, the Pittsburg/Bay Point station located on Bailey Road and Highway 4 near Bay Point and the Pittsburg Center Station located on Railroad Avenue and Highway 4. Tri Delta Transit provides bus service in the area. California State Route 4 bisects the city from west to east.

Pittsburg is twinned with: