Area codes 707 and 369

Major cities in the area codes include Napa, Sebastopol, Vallejo, Benicia, Fairfield, Santa Rosa, Windsor, Healdsburg, Rohnert Park, Petaluma, Fort Bragg, Rio Vista, Crescent City, Eureka, Clearlake, Vacaville, Dixon, and Ukiah.

When the American Telephone and Telegraph Company (AT&T) devised the first comprehensive telephone numbering plan for the North American continent in 1947, the far northern part of California received area code 916, with the exclusion of the city of Sacramento, which used area code 415.

707 was the last of California's thirteen area codes with only 0 or 1 in middle position, the others being 310, 510, 818 and 909, all of which, in addition to 619, were introduced decades after 707's debut) to require relief from a "new format" area code (those with 2–8 as their middle digit, which were introduced beginning in 1995 when the NANP ran out of the original format NPAs), despite explosive growth in the area, particularly its southern portion, as well as the proliferation of cell phones and pagers.

Still, after twenty more years of continued growth in the region, it was determined that 707 would indeed require relief.

On August 1, 2022, the NANP Administrator set the effective implementation date of the overlay of 707 by the new 369 NPA to February 1, 2023.