The United States began centrally recording alien data on April 1, 1944, with single files containing all records of a given alien, according to the U.S. Citizenship and Immigration Services. It is possible to obtain an Alien File, or A-file, through a USCIS Genealogy or Freedom of Information Act request.
If Genealogy and FOIA requests do not procure the desired results, a searcher may also submit a request to the National Archives, commonly referred to as NARA. This is particularly pertinent for immigration cases prior to April 1, 1944, explains the USCIS website at USCIS.gov. Not all files exist, particularly with exclusion cases in which the alien was denied entrance altogether.