From USCIS and Alien Voting: Falling Down on the Job, ImmigrationReform.com, July 7, 2017:
With very limited exceptions, U.S. citizenship is required to vote in an American election. It is a crime for non-citizens to vote in a federal election. And aliens who do so may be charged with a crime pursuant to 18 U.S. Code Section 1611. Similarly, an alien who makes a false claim to U.S. citizenship in order to vote may be prosecuted pursuant to 18 U.S. Code Section 1015(f).
Pursuant to the terms of the Immigration and Nationality Act (INA), any alien who has voted in violation of any federal, state or local constitutional provision, statute, ordinance, or regulation is both inadmissible and deportable.