National Archives and Records Administration (NARA)
NARA is the nation's record keeper. Of all documents and materials created in the course of business conducted by the United States Federal government, only 1%-3% are so important for legal or historical reasons that they are kept forever.
Those valuable records are preserved and are available to you, whether you want to see if they contain clues about your family’s history, need to prove a veteran’s military service, or are researching a historical topic that interests you. Link takes you to the National Archives site.
National Parks Service Soliders and Sailors Database - The Civil War
The database has information about men who served in the Union and Confederate armies, histories of regiments, links to battles, prisoner-of-war records and cemeteries. CWSS is a cooperative effort between the NPS and public and private partners.
Social Security Death Index
U.S., Social Security Death Index, 1935-2014. The link takes you Ancestry.com