Per the ACLU: The act of being present in the United States in violation of the immigration laws is not, standing alone, a crime. While federal immigration law does criminalize some actions that may be related to undocumented presence in the United States, undocumented presence alone is not a violation of federal criminal law. Thus, many believe that the term “illegal alien,” which may suggest a criminal violation, is inaccurate or misleading. 

Undocumented presence in the United States is only criminally punishable if it occurs after an individual was previously formally removed from the United States and then returned without permission. Mere undocumented presence in the United States alone, however, in the absence of a previous removal order and unauthorized reentry, is not a crime under federal law.

If you are an Immigrant, know your rights: https://www.aclu.org/know-your-rights/immigrants-rights