Area codes in northwestern California, United States
Numbering plan areas in California (blue) and border states. This map is clickable; click on any region shown to visit the page for those area codes.Area code 707 is shown in red.
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. California area codes were reorganized geographically in 1950, so that 916 was assigned to a numbering plan area that comprised only the northeastern part from the Sierra Nevada to the Central Valley. The coastal area to the west was assigned area code 415. With this change, Sacramento was also changed to area code 916.
On March 1, 1959, numbering plan area 415 was divided in a flash-cut (without permissive dialing period) in which the northern part of the numbering plan area (Solano County and north thereof) received area code 707, which was California's eighth area code (along with 213, 415, 916, 714, 408, 805, and 209), and the last new area code in the state until 619 was added in 1982.
When area code 530 was split from area code 916 on November 1, 1997, the Dixon area was renumbered from area code 916 to 707 and switched from the Sacramento local access and transport area (LATA) into the San Francisco LATA.
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.
In 1999, a three-way, two-phase split of area code 707 was scheduled by Pacific Bell[1] such that a new area code (627) would have served most of Napa and Sonoma counties and small portions of Marin and Mendocino counties, while another new area code (369) would have served Solano County as well as a small portion of Napa County, beginning in December 2000 and October 2001, respectively. However, due to the success of number pooling in preserving numbering resources, the California Public Utilities Commission cancelled these actions on July 27, 2000. 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.[2]
