The California 209 area code covers cities including Lodi, Merced, Modesto and Stockton. The 209 area code covers a large area of mostly rural California in the Central Valley and Sierra Foothills. The 209 area is east of San Francisco, south of Sacramento and north of Fresno.
Authorities split area code 209 from area code 916 in 1958. Area code 916 covers only Sacramento as of 2015. Authorities split area code 209 itself in 1999. Area code 559 covers the southern Central Valley along with the city of Fresno.
Other cities in the 209 area code include Tracy, Ceres, Galt and Turlock. Modesto is the largest city in area code 209.
New area codes are necessary when a rise in population results in an increased demand for phone numbers, states AreaCodeHelp.com. The North American Numbering Plan Administration manages area codes on the continent. The Federal Communications Commission has jurisdiction over telephone number administration in the United States.
AT&T and Bell Laboratories developed area codes in the 1940s and introduced them in 1947, reports The Atlantic. Area codes helped to automate phone systems, which up until that point relied almost entirely on human operators. The all-number system replaced a mixed categorization system of numbers, letters and words.