Contra Costa County, California

Contra Costa County is a county in California, United States, in the East Bay of the San Francisco Bay Area, about 25 miles northeast of San Francisco. It had a population of 1,165,927 at the 2020 census, an estimated 1,170,070 by 2025, and covers 716 square miles (1,854 km2) of land centred near 37°56′N 121°57′W.

Martinez is the county seat; its postal code is 94553. The county holds 18 cities and 1 incorporated town, plus 20 recognized unincorporated communities, and it runs on Pacific Time. Its FIPS code is 06013.

Towns & Villages in Contra Costa County

Contra Costa County has 39 named places on record: 19 incorporated cities and towns and 20 unincorporated communities recognized by the Census Bureau as CDPs, short for census designated place, with no local government of their own. California has no civil townships, so the table below runs Place, Type, Pop. and ZIP only. Several dozen smaller unincorporated place names — rail sidings, old refinery camps and subdivisions such as Clyde, Vine Hill, Rollingwood and Norris Canyon — appear in federal gazetteer records with no separate population count and are not listed here.

Two pairs on this list share a ZIP with a neighbor rather than carrying their own. Bay Point uses Pittsburg’s 94565, a leftover from its earlier name, West Pittsburg, which the community dropped in 1993. Tara Hills and North Richmond both use their larger neighbors’ codes — San Pablo’s 94806 and Richmond’s 94801 — rather than a code of their own.

ZIP Codes

• 94518 — Concord
• 94801 — Richmond (also serves North Richmond)
• 94509 — Antioch
• 94583 — San Ramon
• 94565 — Pittsburg (also serves Bay Point)
• 94595 — Walnut Creek
• 94513 — Brentwood
• 94526 — Danville
• 94561 — Oakley
• 94553 — Martinez (also serves Pacheco)
• 94523 — Pleasant Hill
• 94806 — San Pablo (also serves Tara Hills)
• 94547 — Hercules
• 94530 — El Cerrito
• 94549 — Lafayette
• 94563 — Orinda
• 94564 — Pinole
• 94556 — Moraga
• 94517 — Clayton
• 94803 — El Sobrante
• 94505 — Discovery Bay
• 94507 — Alamo
• 94572 — Rodeo
• 94707 — Kensington
• 94525 — Crockett
• 94548 — Knightsen
• 94528 — Diablo
• 94569 — Port Costa

Blackhawk, Camino Tassajara, Montalvin Manor, Bayview, Acalanes Ridge, Byron and Alhambra Valley have no ZIP code confirmed as their own; mail there is delivered under a neighboring town’s code.

Geography

Contra Costa County stretches from the Carquinez Strait shoreline in the north to Mount Diablo, at 3,849 feet the dominant peak of the East Bay, near its center. West-county land along San Pablo and San Francisco bays is flat and urbanized; the middle of the county rises into the oak-covered ridgelines around Walnut Creek, Lafayette, Orinda and the Berkeley Hills; the east county flattens again into the Sacramento–San Joaquin River Delta around Discovery Bay, Bethel Island and Knightsen, a landscape of levees, sloughs and reclaimed farmland. Of the county’s 804 square miles, 716 are land and 88 are water — the Carquinez Strait, Suisun Bay and San Pablo Bay along the north and west edge, plus the Delta channels in the east. Mount Diablo also served as the base point for the Mount Diablo Meridian, the survey reference line used to map most of California and Nevada.

Solano County lies to the north and northeast across the Carquinez Strait, Sacramento County borders a short stretch of the northeast corner in the Delta, San Joaquin County lies to the east, and Alameda County lies to the south. Solano County, Sacramento County, San Joaquin County and Alameda County all border Contra Costa directly.

Demographics

Contra Costa County had a population of 1,165,927 at the 2020 census, and the latest estimate puts the county near 1,170,070 residents. Concord and Richmond are the two largest cities, together holding well over 200,000 residents. Median household income runs $127,229, notably higher than California’s statewide figure of $95,521. Population density works out to roughly 1,630 people per square mile of land, among the denser counties in the Bay Area outside Alameda and San Francisco, reflecting the county’s position inside the San Francisco–Oakland–Berkeley combined statistical area.

Economy & Local Life

Health care and social assistance employs the most workers in the county, about 80,112 people, followed by professional, scientific and technical services at 72,459 and retail trade at 58,386. The Chevron Richmond Refinery, one of the largest oil refineries on the West Coast, anchors much of Richmond’s industrial employment, and Phillips 66’s Rodeo refinery and the Martinez Refining Company add to the county’s refining sector along the Carquinez Strait. Chevron Corporation is headquartered at Bishop Ranch, a large office park in San Ramon that also houses several other national and regional company offices. Bio-Rad Laboratories, a life-sciences and diagnostics maker, is headquartered in Hercules, and John Muir Health and Kaiser Permanente both run major hospital campuses in Walnut Creek. The county’s biggest annual event is the Contra Costa County Fair, held each June in Antioch.

History

California’s first state legislature created Contra Costa County on 18 February 1850, one of the state’s original 27 counties at statehood. The name is Spanish for “opposite coast,” describing the county’s position across San Francisco Bay from the city of San Francisco. Martinez, platted in 1849 on land granted to the Martinez family, became the county seat in 1850 and has held that role ever since.

On 17 July 1944, an explosion at the Port Chicago Naval Magazine, near present-day Concord, killed 320 sailors and civilians loading munitions onto cargo ships bound for the Pacific; most of the dead were Black enlisted sailors. When 258 survivors refused orders to resume loading ammunition under the same unsafe conditions, the Navy court-martialed 50 of them for mutiny. The Port Chicago case became a rallying point for civil-rights advocates and is widely credited as a catalyst for the desegregation of the U.S. Navy, formalized in 1946.

Getting There

Interstate 80 crosses the county’s northwest corner through Richmond, San Pablo, Pinole and Hercules. Interstate 680 runs north–south through the center of the county via Martinez, Walnut Creek, Danville and San Ramon, and Interstate 580 crosses Richmond on its way to the Richmond–San Rafael Bridge. State Route 4 runs east–west through Concord, Pittsburg and Antioch toward the Delta, and State Route 24 links Oakland to Walnut Creek through the Caldecott Tunnel.

• Oakland — about 15 miles south
• San Francisco — about 25 miles west
• San Jose — about 45 miles south
• Sacramento — about 50 miles northeast

Oakland International Airport, about 20 miles south of Martinez, is the nearest major commercial airport; San Francisco International Airport lies roughly 30 miles southwest. BART rapid transit serves stations across the county including Richmond, El Cerrito, Orinda, Lafayette, Walnut Creek, Concord, Pleasant Hill and Antioch, and Amtrak’s Capitol Corridor and San Joaquins trains stop at the Martinez station.

Frequently Asked Questions

Where is Contra Costa County located?
It sits in the East Bay of the San Francisco Bay Area, about 25 miles northeast of San Francisco, bordered by Solano, Sacramento, San Joaquin and Alameda counties.

What is the population of Contra Costa County?
1,165,927 at the 2020 census, with a 2025 estimate near 1,170,070.

How big is Contra Costa County?
804 square miles total (716 square miles of land and 88 square miles of water), or 1,854 km2 of land.

What is the county seat of Contra Costa County?
Martinez, the county seat since 1850.

How many towns and cities are in Contra Costa County?
18 cities and 1 incorporated town — led by Concord, Richmond and Antioch — plus 20 unincorporated communities recognized as census designated places, from Bay Point down to Port Costa.

What ZIP codes does Contra Costa County use?
Every incorporated city has its own ZIP, from 94509 in Antioch to 94595 in Walnut Creek; several unincorporated communities such as Bay Point and Pacheco share a neighboring city’s code instead of having one of their own.

What is Contra Costa County known for?
Mount Diablo, the Chevron Richmond Refinery, and the 1944 Port Chicago disaster, whose mutiny trials became a catalyst for the U.S. Navy’s 1946 desegregation.

More counties in this state: Towns and villages in California.