8 U.S.C. § 1409: Children born out of wedlock

a blood relationship between the person and the father is established by clear and convincing evidence, the father had the nationality of the United States at the time of the person’s birth, the father (unless deceased) has agreed in writing to provide financial support for the person until the person reaches the age of 18 years, and the person is legitimated under the law of the person’s residence or domicile, the father acknowledges paternity of the person in writing under oath, or the paternity of the person is established by adjudication of a competent court. Except as otherwise provided in section 405 of this Act, the provisions of section 1401(g) of this title shall apply to a child born out of wedlock on or after January 13, 1941 , and before December 24, 1952 , as of the date of birth, if the paternity of such child is established at any time while such child is under the age of twenty-one years by legitimation. Notwithstanding the provision of subsection (a) of this section, a person born, after December 23, 1952 , outside the United States and out of wedlock shall be held to have acquired at birth the nationality status of his mother, if the mother had the nationality of the United States at the time of such person’s birth, and if the mother had previously been physically present in the United States or one of its outlying possessions for a continuous period of one year. Except as provided in paragraph (2)(B), the new section 309(a) [ 8 U.S.C. 1409(a) ] (as defined in paragraph (4)(A)) shall apply to persons who have not attained 18 years of age as of the date of the enactment of this Act [ Nov. 14, 1986 ]. to any individual who has attained 18 years of age as of the date of the enactment of this Act, and any individual with respect to whom paternity was established by legitimation before such date. An individual who is at least 15 years of age, but under 18 years of age, as of the date of the enactment of this Act, may elect to have the old section 309(a) apply to the individual instead of the new section 309(a). The term ‘new section 309(a)’ means section 309(a) of the Immigration and Nationality Act [ 8 U.S.C. 1409(a) ], as amended by section 13 of this Act [ section 13 of Pub. L. 99–653 ] and as in effect after the date of the enactment of this Act. The term ‘old section 309(a)’ means section 309(a) of the Immigration and Nationality Act, as in effect before the date of the enactment of this Act.”