How do the police make a determination if somebody is here illegally or not? There is no law which requires anyone to carry ID unless they are foreigners here on a visa. If an illegal alien speaks English without an accent and provides their name upon request by the police, then there is likely no probable cause that they are illegal. No one has to answer questions of the police without an attorney present. You don't have to say who your parents are or where they are from. Just try to stay out of trouble and don't go demanding any privilages of residency or citizenship.