Gather the person's full name, date of birth, country of birth, and alien number
The person's full name, date of birth, country of birth, and alien number are very important to finding someone in immigration detention. The full name includes middle names and all last names. You don't have to know the alien number, but it makes the process much easier. The alien number appears on all paperwork from the government. It contains eight or nine digits, and usually appears with the letter A in front. It will also appear in the person's U.S. visa, if the person has one. If the person's passport has not been seized by ICE, find it and keep it in a safe place. It will likely be very important in the person's immigration case.
Use the Online Detainee Locator System (ODLS)
ICE maintains a system system online to search for individuals in immigration detention. http://www.ice.gov/locator/ If searching by name, try several different variations. For example, you may call the person "Luis Lopez." You enter that name and nothing appears. But his full name may be "Jose Luis Lopez Diaz." Try searching for "Jose" as the first name and "Lopez Diaz" as the last name, and other variations.
If ODLS comes up negative, consider whether the person could be somewhere else
ODLS only shows information about people physically in ICE custody. It does not show information about people with an "immigration hold" that are physically in the custody of a local jail, or a state or federal prison. It also does not show information about people who already have been removed from the United States.
Check with the federal Bureau of Prisons
Reentering the United States after being deported is a federal crime. The person you are looking for could have been charged with a federal crime and brought into a federal district court instead of being placed in immigration proceedings. Illegal reentry cases are (unfortunately) typically disposed of quickly by guilty plea, and the person is then incarcerated by the Bureau of Prisons, which maintains an inmate locator here: http://www.bop.gov/iloc2/LocateInmate.jsp
Call the Immigration Court's automated information line
If you have the person's alien number, you can also call the Immigration Court's automated information line at (800) 898-7180. Enter the person's number, then hit 1 to confirm the name, then select both option 1 for the person's next court appearance, and then select option 3 for decision information. If the person has a court date but is not listed in OLDS, they could be out on bond or not subject to detention. If the person has decision information on file, the person could have already been removed from the United States.
Call a lawyer
The U.S. has the most complex and harsh immigration laws on the planet. Don't make the mistake of trying to navigate that system without a professional. Immigration cases can have consequences that last a person's entire life. Spend the time and the money to make sure that everything possible is done for your loved one.