A derivative citizenship is one that is derived from the citizenship of the parent, usually the father. In the easiest of cases, foreign born children under the age of majority when their father naturalized would be considered naturalized themselves and would not have to go through the process themselves.
If your ancestor immigrated as a child, indicates he is naturalized but you cannot find any papers in his name, then consider the possibility that he had derivative citizenship through a father’s naturalization.
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In attempting to find out if my stepfather's mother had been natuaralized, I discovered that if an immigrant lady married a U.S. citizen husband prior to September 22, 1922, she also derived citizenship through her marriage. In this instance, she had married a U.S. citizen in 1898, so she had derivative citizenship. This information came from the U.S. Citizenship and Immigration Services.
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