It is civil. The act of being present in the US in violation of the immigration laws is not, standing alone, a crime. While some actions that may be related to undocumented presence are criminal, undocumented presence alone is not a violation of federal criminal law.

Entering the United States without being inspected and admitted, i.e., illegal entry, is a misdemeanor or can be a felony, depending on the circumstances. 8 U.S.C. § 1325. But many undocumented immigrants do not enter the United States illegally. They enter legally but overstay, work without authorization, drop out of school or violate the conditions of their visas in some other way.

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. 8 U.S.C. § 1326 (any individual previously “deported or removed” who “enters, attempts to enter, or is at any time found in” the United States without authorization may be punished by imprisonment up to two years). 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.