While many websites specialize in people-finding will try sell you information regarding a person's criminal or prison record, you easily can obtain data on a person's current or past incarceration from official sources without paying a dime. Complete data on all federal inmates is easily available at no charge online. Many individual states, as well, offer searchable databases of their inmates, allowing you to see when and where a specific person was in prison.
Go to the Federal Bureau of Prisons' searchable inmate database. Any person in federal prison at any time since 1982 can be found within the files. Simply enter a complete name, together with any other known information, and click the "Search" button. If you know the inmate's ID number, you can search by that instead. The search will give you the name, register number, age, race, sex, date of release and current location---if still imprisoned---of the inmate in question.
Write a letter to the National Archives if you're looking for information on a prisoner who was released before 1982. Include the prisoner's name, date of birth and race in your correspondence, together with an estimate of the years spent in prison. Address it to:
Federal Bureau of Prisons
Office of Communications and Archives
Attn: Historic Inmate Locator Request
320 First St., N.W.
Washington, DC 20534
Use your state's inmate locator tool, if you're looking for someone incarcerated in a non-federal prison. While not all state department of corrections websites contain such a database, many do. To find yours, go to the USA.gov's State Corrections Departments website, click on your state's name, click on the link to the website of the state department of corrections and browse the site for an inmate locator. Because each such site is maintained by each own state, the information available will vary widely.