In the United States, a Social Security number (SSN) is a nine-digit number issued to U.S. citizens, permanent residents, and temporary (working) residents under section 205(c)(2) of the Social Security Act, codified as . The number is issued to an individual by the Social Security Administration, an independent agency of the United States government. Although its primary purpose is to track individuals for Social Security purposes, the Social Security number has become a de facto national identification number for taxation and other purposes.
A Social Security number may be obtained by applying on Form SS-5, Application for A Social Security Number Card.
Social Security numbers were first issued by the Social Security Administration in November 1935 as part of the New Deal Social Security program. Within three months, 25 million numbers were issued.
On November 24, 1936, 1,074 of the nation's 45,000 post offices were designated "typing centers" to type up Social Security cards that were then sent to Washington, D.C. On December 1, 1936, as part of the publicity campaign for the new program, Joseph L. Fay of the Social Security Administration selected a record from the top of the first stack of 1,000 records and announced that the first Social Security number in history was assigned to John David Sweeney, Jr., of New Rochelle, New York.
Before 1986, people often did not obtain a Social Security number until the age of about 14, since the numbers were used for income tracking purposes, and those under that age seldom had substantial income. The Tax Reform Act of 1986 required parents to list Social Security numbers for each dependent over the age of 5 for whom the parent wanted to claim a tax deduction. Before this act, parents claiming tax deductions were on the honor system not to lie about the number of children they supported. During the first year of the Tax Reform Act, this anti-fraud change resulted in seven million fewer minor dependents being claimed. The disappearance of these dependents is believed to have involved either children who never existed or tax deductions improperly claimed by non-custodial parents. In 1988, the threshold was lowered to 2 years old, and in 1990, the threshold was lowered yet again to 1 year old. Today, a SSN is required regardless of the child's age to receive an exemption. Since then, parents have often applied for Social Security numbers for their children soon after birth; today, it can be done on the application for a birth certificate.