When someone dies in the United States, a family member, attorney, or mortician typically reports the death to the United States Social Security Administration in connection with filing for death benefits.
The information about the deceased is then recorded in the Social Security Administration's Death Master File (DMF). The DMF currently contains more than 94 million records. The index for the DMF is a database called the Social Security Death Index (SSDI).
The SSDI is a popular tool for genealogists and biographers because it contains valuable genealogical data.
What genealogical data can I learn from the Social Security Death Index?
Name of the deceased (married women usually by married name)
State (or territory) where their Social Security Number was issued
Death residence with zip code (last place of residence on file but not necessarily the place of death)
When two geographical names are listed they represent the county and state (not the city and state). The city may be determined by using the zip code.
What years does it cover?
The SSDI has a few deaths from 1935 to 1961, about 50% of the deceased from 1962 to 1971, and about 85% of the deceased from 1972 to 2005.