There are several websites where one can search for death records online for free. The Vital Records portion of the National Archives website is a good place to begin. Another option is Family Search.
The National Archives website, archives.org, offers links to many military and census records. The indexes are separated specific to certain states. However, through the Family Search online database, users can search death records or other genealogical events by last names and years. Additional information, such as birthplace, place of residence at death, spouse information and marriage information, helps provide more narrowed results. It is recommended to search the website of the county of residency of the subject, as it may provide information on public vital records.