If you are applying for a green card in the United States by adjustment of status after marrying a U.S. citizen, you'll notice that one question on the application Form I-485 asks: "Have you ever, in or outside the United States: Been arrested, cited, charged, indicted, convicted, fined, or imprisoned for breaking or violating any law or ordinance, excluding traffic violations?"
This leads to questions among applicants who, for example, were arrested a long time ago in their overseas hometown, but where the charge was later withdrawn. They often wonder whether they can avoid complicating their case by bringing up the past; or whether USCIS will find out about the arrest and regard this as a lie. That's what this article will address.
Historically, U.S. government access to foreign criminal records (other than Canada's) has been limited. Therefore, if you do not tell USCIS about your arrest, there is a chance that the agency will not find out about it.
Nevertheless, given how quickly information-sharing technologies and policies can change, and how serious the consequences for failing to disclose one's criminal background can be, you would be taking a chance on this.
For adjustment of status applicants who have been associated with national security threats or organized crime, records of foreign convictions might already be available to USCIS through U.S. government databases and could be retrieved automatically after the biometrics appointment.
For all other adjustment applicants, USCIS would need to make an individual records request through Interpol. That's unlikely to happen unless an application raises particular suspicions. Add to this the fact that foreign governments might be reluctant to share records of arrests and charges that did not result in a conviction, and you could reasonably conclude that USCIS is unlikely to find out about your criminal history.
Even the remote chance that USCIS might find out about that background should dissuade you from answering "No" to the Form I-485 question about your previous arrest and charge.
Your record could be revealed, for example, if you traveled outside the U.S. one day and were required, for one reason or another, to apply for an immigrant visa in order to reenter the country. In this case, you might also need to submit a police certificate with your visa application. As a result, you would be found inadmissible to the U.S. on grounds of "willful misrepresentation"; in other words, for failing to disclose your criminal background. (And, even assuming you managed to obtain a waiver for this bar, your future access to U.S. citizenship could be jeopardized for lack of "good moral character.")
These risks seem unnecessary, especially because, in the absence of aggravating factors, many minor crimes would not make you inadmissible even if you were eventually found guilty (or pled guilty); though USCIS would still want to judge for itself your explanation of the circumstances of your arrest and dismissal.
When in doubt, especially about something as complex as the overlay of criminal and immigration law, hiring an attorney to help with your green card application can make your life much easier. See How Expensive Is an Immigration Lawyer?