38 articles
Alameda County, California
Alameda County, California: East Bay county established 1853, seat Oakland, 14 cities, 1,682,353 residents (2020), seventh most populous in California, $6.7B FY 2026-27 budget, AAA credit rating.
Clark County, Nevada
Clark County, Nevada: county containing Las Vegas, its county seat. Created 1909 from Lincoln County, named for Senator William Andrews Clark. Nevada's most populous county, 2.4 million residents, gaming and tourism economy.
Coconino County, Arizona
Coconino County, Arizona: county in northern Arizona, seat Flagstaff, created 1891 from Yavapai County. Largest Arizona county at 18,616 sq mi, 145,101 people (2020), home to the Grand Canyon and San Francisco Peaks.
Contra Costa County, California
Contra Costa County, California: an original 27-county East Bay county created February 18, 1850, named Spanish for 'opposite coast,' county seat Martinez, about 1.17 million residents, ninth most populous, bounded by San Francisco, San Pablo, and Suisun bays.
Doña Ana County
Doña Ana County, New Mexico: county seat Las Cruces, FIPS 35013, formed 1852, named for village of Doña Ana and Doña Ana María de Córdoba; 219,561 people (2020), 68.3% Hispanic, 45-mile Mexico border, Project Jupiter data center.
Fresno County, California
Fresno County, California: a San Joaquin Valley county formed in 1856, seat at Fresno, population about 1.04 million, sixth-largest county by area, and the top U.S. county for agricultural sales.
Humboldt County, California
Humboldt County, California: North Coast county with seat Eureka, formed 1853 from Trinity County, named for Alexander von Humboldt; 136,463 people in 2020, redwood forests, Humboldt Bay port, and Emerald Triangle cannabis country.
Imperial County, California
Imperial County, California: southeastern border county (seat El Centro, est. 1907, pop. ~180,000) known for Imperial Valley winter-vegetable farming, Colorado River water via the Imperial Irrigation District, the Salton Sea, geothermal energy, and the Lithium Valley development effort.
Inyo County, California
Inyo County is a rural county in eastern California, established in 1866 with its seat at Independence, holding both Mount Whitney, the highest peak in the lower 48 states, and Badwater Basin.
Kern County, California
Kern County, California: county at the southern Central Valley and Mojave Desert, seat Bakersfield, founded 1866. Over 70 percent of state oil output, a top-five US farm county, population about 927,000.
List of counties in Arizona
Arizona's 15 counties, from the four original 1863 counties (Mohave, Pima, Yavapai, Yuma) through short-lived Pah-Ute County to La Paz County (1983) and later proposals to divide Maricopa County.
List of counties in California
California's 58 counties: 27 original counties created February 1850, Imperial County the last in 1907; 43 general law and 15 charter counties, with San Francisco a consolidated city-county.
List of counties in Washington
List of counties in Washington: the 39 counties of Washington State with their county seats, from Adams (Ritzville) to Yakima (Yakima); King County is most populous, Garfield least, Okanogan largest, San Juan smallest.
Maricopa County, Arizona
Maricopa County, Arizona: county seat Phoenix; established 1871; 4.5 million residents, 4th largest US county, 62% of Arizona's population; 9,224 square miles; five-member Board of Supervisors; swing-county election disputes.
Marin County, California
Marin County, California: Bay Area county north of San Francisco, established 1850 as one of the state's original 27 counties. Seat San Rafael; 520 square miles; 11 incorporated towns; Coast Miwok homeland; about 254,000 residents.
Mendocino County, California
Mendocino County is a northern California county established in 1850, seat at Ukiah, population about 88,000-91,600, known for redwoods, coastline, wine grapes, and a documented structural budget deficit.
Mohave County
Mohave County, Arizona: northwestern county, county seat Kingman; one of Arizona's four original 1864 counties, second largest in the state at about 13,470 square miles; 228,102 residents (2025 est.); home of London Bridge, Route 66, Grand Canyon West.
Monterey County, California
Monterey County, California: original 1850 county on the central coast, seat Salinas. 439,035 residents (2020), 62.9% Hispanic, $11.7 billion agriculture, major defense and tourism economy.
Multnomah County, Oregon
Multnomah County, Oregon: Portland-seat county created December 22, 1854 as Oregon Territory's 13th county; smallest by area at 465 square miles, most populous of Oregon's 36 counties, governed by a home rule charter with a countywide Chair and four district commissioners.
Napa County, California
Napa County, California: a San Francisco Bay Area county established 1850, county seat Napa, population about 133,000 (2025 estimate), famed for Napa Valley wine, the 1968 Agriculture Preserve, and recurring wildfire risk.
Nye County, Nevada
Nye County, Nevada: the state's largest county by land area (18,181.9 sq mi) and third-largest in the contiguous U.S., county seat Tonopah, created 1864 from Esmeralda County, population 51,591 (2020).
Pierce County, Washington
Pierce County, Washington: county created December 22, 1852 from Thurston County, named for President Franklin Pierce; seat Tacoma; second most populous Washington county (921,130 in 2020), home to Mount Rainier, JBLM, and the Port of Tacoma.
Pima County, Arizona
Pima County, Arizona: second-most populous Arizona county, county seat Tucson, one of four original 1864 territorial counties. Covers 9,189 sq mi, population 1,043,433 (2020), FY2026/27 budget $1.809 billion.
Riverside County, California
Riverside County, California: county formed May 9, 1893 from San Bernardino and San Diego counties, seat at Riverside city. Fourth-largest California county, about 2.5 million residents, logistics- and tourism-driven Inland Empire economy.
Sacramento County, California
Sacramento County, California: a 994-square-mile Central Valley county founded 1850, seat of California state government, seven incorporated cities, population about 1.6 million.
San Bernardino County, California
San Bernardino County is a county in Southern California, created from Los Angeles County in 1853. It is the largest US county by area and had 2,181,654 residents in 2020.
San Diego County, California
San Diego County, California: southwesternmost California county on the Mexico border, established 1850, second most populous of 58 counties, 3.28 million residents, $8.63 billion FY 2025-26 budget, $266.9 billion regional economy.
San Joaquin County, California
San Joaquin County, California: Central Valley county established 1850, county seat Stockton, eight cities, 823,815 residents (2025 est.), $3.15 billion agriculture, Port of Stockton, governed by a five-member Board of Supervisors.
San Luis Obispo County, California
San Luis Obispo County is a Central Coast California county, one of the original 27 counties (1850), seat at San Luis Obispo, population 282,424 (2020), 3,300 square miles, 100 miles of coastline.
Santa Barbara County, California
Santa Barbara County, California: coastal county, county seat Santa Barbara, one of the original 27 counties created February 18, 1850, named for Mission Santa Barbara (1786); 2020 population 448,229.