Section 216(h)(1) of the Social Security Act provides that an applicant is the wife of an insured individual for purposes of such Act if the courts of the State in which such insured individual is domiciled at the time the application for wife's insurance benefits is filed would find that the applicant and such insured individual were validly married.
SSA does accept Common Law Marriages if the marriage was in a state that recognizes same.
Evidence of Common-Law Marriage
1717.1How do you prove a common-law marriage?
Evidence to prove a common-law marriage in the States that recognize such marriages must include:
If the husband and wife are living, a statement from each and a statement from a blood relative of each;
If either the husband or wife is dead, a statement from the surviving widow or widower and statements from two blood relatives of the decedent; or
If both a husband and wife are dead, a statement from a blood relative of the husband and from a blood relative of the wife.
1717.2How should the statements be made?
The statements of the husband, wife, and relatives must be made on special forms, Statement Regarding Marriage or Statement of Marital Relationship, available at any Social Security office or on the Social Security Administration's website. You must fully answer all items on the forms and in your own words. Also, submit evidence that confirms that you had a common-law marriage, such as mortgage/rent receipts, bank records, insurance policies, etc.