In 1947, the State of California enacted the Air Pollution Control Act that authorized the creation of Air Pollution Control Districts (APCD) or Air Quality Management Districts (AQMD) in every county of the State. California has 23 APCD and 12 AQMDs for a total of 35 districts:

• Amador County APCD (all of Amador County)
• Antelope Valley AQMD (Northeast portion of Los Angeles County)
• Bay Area AQMD
  Bay Area Air Quality Management District
  The Bay Area Air Quality Management District is a public agency that regulates the stationary sources of air pollution in the nine counties of California's San Francisco Bay Area: Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, southwestern Solano, and southern Sonoma...
  
  (Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, western portion of Solano, southern portion of Sonoma counties)
• Butte County AQMD (all of Butte County)
• Calaveras County APCD (all of Calaveras County)
• Colusa County APCD (all of Colusa County)
• Eastern Kern APCD (Eastern portion of Kern County)
• El Dorado County AQMD (all of El Dorado County)
• Feather River AQMD (all of Sutter and Yuba counties)
• Glenn County APCD (all of Glenn County)
• Great Basin Unified APCD (all of Alpine, Inyo, and Mono counties)
• Imperial County APCD (all of Imperial County)
• Lake County AQMD (all of Lake County)
• Lassen County APCD (all of Lassen County)
• Mariposa County APCD (all of Mariposa County)
• Mendocino County AQMD (all of Mendocino County)
• Modoc County APCD (all of Modoc County)
• Mojave Desert AQMD (Northern portion of San Bernardino County, eastern portion of Riverside County)
• Monterey Bay Unified APCD (all of Monterey, San Benito, Santa Cruz counties)
• North Coast Unified AQMD (all of Del Norte, Humboldt, Trinity counties)
• Northern Sierra AQMD (all of Nevada, Plumas, Sierra counties)
• Northern Sonoma County APCD (Northern portion of Sonoma County)
• Placer County APCD (all of Placer County)
• Sacramento Metro AQMD (all of Sacramento County)
• San Diego County APCD (all of San Diego County)
• San Joaquin Valley APCD (all of Fresno, Kings, Madera, Merced, San Joaquin, Stanislaus, Tulare, and Valley air basin portions of Kern counties)
• San Luis Obispo County APCD (all of San Luis Obispo County)
• Santa Barbara County APCD (all of Santa Barbara County)
• Shasta County AQMD (all of Shasta County)
• Siskiyou County APCD (all of Siskiyou County)
• South Coast AQMD
  South Coast Air Quality Management District
  The South Coast Air Quality Management District , formed in 1976, is the air pollution agency responsible mainly for regulating stationary sources of air pollution for most of Los Angeles, San Bernardino, Riverside County, and all of Orange County...
  
  (Los Angeles County except for Antelope Valley AQMD, Orange County, western portion of San Bernardino and western portion of Riverside counties)
• Tehama County APCD (all of Tehama County)
• Tuolumne County APCD (all of Tuolumne County)
• Ventura County APCD
  Ventura County Air Pollution Control District
  The Ventura County Air Pollution Control District , formed in 1968, is the air pollution agency responsible mainly for regulating stationary sources of air pollution for Ventura County...
  
  (all of Ventura County)
• Yolo-Solano AQMD (all of Yolo and eastern portion of Solano counties)

History

The California Air Pollution Control District Act of 1947 allowed 1 or more counties to form air pollution districts. The California Bay Area Pollution Control Act of 1955 created the Bay Area Air Pollution Control District. The California Mulford-Carrell Air Resources Act of 1967 resulted in the creation of 11 air basins.