20 CFR §404.770

1. (a)When evidence of the insured's permanent home is needed. We may ask for evidence of where the insured person's permanent home was at the time you applied or, if earlier, the time he or she died if—
   1. (1)You apply for benefits as the insured's wife, husband, widow, widower, parent or child; and
   2. (2)Your relationship to the insured depends upon the State law that would be followed in the place where the insured had his or her permanent home when you applied for benefits or when he or she died.
2. (b)What evidence is needed. We will ask for the following evidence of the insured person's permanent home:
   1. (1)Your signed statement showing where the insured considered his permanent home to be.
   2. (2)If the statement in paragraph (b)(1) of this section or other evidence we have raises a reasonable doubt about where the insured's permanent home was, evidence of where he or she paid personal, property, or income taxes, or voted; or other convincing evidence of where his or her permanent home was.