20 CFR 416.1600: Introduction.

You are eligible for supplemental security income (SSI) benefits if you meet the requirements in subpart B. Among these are requirements that you must be a resident of the United States and either a citizen, a national, or an alien with a lawful right to reside permanently in the United States. In this subpart, we tell you what kinds of evidence show that you are a resident of the United States (see § 416.1603) and—

(a) A citizen or a national of the United States (see § 416.1610);

(b) An alien lawfully admitted for permanent residence in the United States (see § 416.1615); or

(c) An alien permanently residing in the United States under color of law (see § 416.1618).