Complex sentence: Martín de Argüelles, Jr. (born 1566) was the first child of European descent born in a permanent European settlement in what is now the continental United States according to documents and manuscripts in the archives of the Library of Congress.
Split into simpler sentences: Martín de Argüelles, Jr. (born 1566) was the first child born in the Americas of European heritage. This is according to documents and manuscripts in the archives of the Library of Congress.