Martín de Argüelles, Jr. (born 1566) was the first white child (first criollo) known to have been born in what is now the United States. His birthplace St. Augustine, Florida (San Agustín, La Florida) is the oldest continuously occupied, European-founded city in the United States.
Argüelles was born in 1566 in the Spanish settlement of St. Augustine, Florida, approximately twenty-one years before the short-lived colony at Roanoke Island in North Carolina. Martín's parents were Martín de Argüelles (Sr.) and Leonor Morales. His father, Martín Argüelles Sr., an Asturian hidalgo, was one of the expeditioners who came to New Spain in the New World with Captain General Pedro Menéndez de Avilés in 1565. Argüelles Sr. was the first Alcalde (Mayor) of San Agustín, and had been in charge of munitions in the Florida forts of Santa María, San Agustín (now St. Augustine), and Santa Elena.
Martín Argüelles Jr. served the Spanish crown in Portugal and several garrisons and expeditions which embarked in the Spanish Armada which went in search of corsair Francis Drake. He was later transferred in 1594 from Havana, Cuba, to Mérida, Mexico, where he was appointed Executive Officer of the Mérida fortress and coast. Argüelles was married in Mérida.