Three things decide: what the deepfake depicts, why it was made, and where it was published.
Clearly illegal: nonconsensual intimate imagery. The federal TAKE IT DOWN Act (signed May 2025) makes knowingly publishing it a crime, AI-generated or not: up to 2 years, 3 years for minors.
Usually illegal: election deception. California, Texas, and others ban materially deceptive election deepfakes near elections. Fraud using a synthetic identity is fraud, same as any other kind.
Sometimes illegal: commercial impersonation. Tennessee's ELVIS Act protects voice; most states protect name, image, and likeness. A fake celebrity endorsement without consent is actionable.
Usually legal: parody and satire. California's election laws explicitly exempt them, and the First Amendment protects most of it. Sources: Congress.gov, NCSL The gray zone is fan content and memes. Legal until someone is harmed or money changes hands.
Whether a deepfake is illegal depends on the state, the content, and the intent; the honest answer really is 'it depends'.