Castro is principally a Galician and Portuguese topographic or habitational surname. It could identify someone who lived by a castro—a fort or fortified settlement—or someone who came from one of the many places named with that word. The name therefore did not begin with one family or one fortress. Scholarly surname dictionaries also record independent Sephardic Jewish and Italian uses of Castro, so the correct explanation for a particular family depends on its earliest documented place and community.
What Castro Means
The ordinary word castro comes from Latin castrum, “fortress.” The Royal Spanish Academy's dictionary defines it as a fortified settlement in Roman Iberia and gives regional senses referring to remains of pre-Roman settlements in Asturias and heights bearing traces of old fortifications in Galicia. The Portuguese Infopédia toponymic dictionary likewise derives the place-name from Latin castrum and notes its frequent use in Portugal and Galicia, including compound names.
“Fort” is therefore the word's literal meaning, but it is not a claim that every first bearer was a soldier or castle owner. In northwestern Iberian usage, a castro may be an ancient fortified settlement, its visible remains, the hill on which it stood, or a locality named for such a site. The surname could arise from residence near the feature (topographic) or origin in a named settlement (habitational).
Galician and Portuguese Formation
The Dictionary of American Family Names classifies Iberian Castro as Galician and Portuguese and gives both topographic and habitational explanations. The Real Academia Galega's surname guide also recognizes Castro as a standard Galician surname form. Calling Castro “Spanish” is geographically reasonable—Galicia is in Spain, and the surname occurs throughout the country—but “Galician and Portuguese” describes its principal Iberian linguistic setting more precisely.
Many places could supply the name. An official Toponimia de Galicia study of O Castro de Caldelas quotes the place as Santa Maria do Castro de Caldellas in a will dated 14 May 1376 and calls a shoemaker a resident enel Castro de Caldelas in a 1408 document. These are attestations of one place-name, not the first records of the surname. They illustrate why “from Castro” is incomplete until the particular locality is established.
Because castro appears in numerous simple and compound place-names, unrelated people could acquire Castro independently. A shared spelling does not show descent from a single medieval house, and the dictionary meaning cannot identify which Castro place—if any—belonged to a specific lineage.
Sephardic and Italian Origins
The Oxford surname dictionary entry also records Castro among Sephardic Jewish surnames, with the same Iberian topographic or habitational basis. This is a documented use of the surname, not evidence that every Castro family has Sephardic ancestry. That conclusion requires records connecting the family to a Jewish community and cannot be made from a surname list alone.
The same source gives a separate Italian origin: a topographic name for someone living near a fortification or a habitational name from Castro in Lazio. That town became the centre of the Duchy of Castro and was destroyed by papal troops in 1649, as documented by Treccani's archaeological encyclopedia. An Italian Castro line should therefore not automatically be folded into a Galician or Portuguese one merely because the spelling and Latin root match.
Castro and De Castro
De Castro is a closely related Galician and Portuguese habitational form. Here de means “of” or “from,” as the Oxford dictionary's De Castro entry explains. Older records may vary in capitalization or spacing, but Castro and de Castro should both be recorded exactly as the documents present them.
The particle de does not by itself prove nobility. It expresses a relationship to a place; a claim of descent from a titled or historically prominent de Castro family needs a documented genealogical chain to that particular family. Nor should Castrillo, Castillo, Del Castro, or accented Castró be silently treated as spellings of Castro: similar appearance or meaning is not enough to establish that two surnames are variants in a given record set.
Present Distribution in Spain
Spain's National Statistics Institute recorded 123,156 residents with Castro as their first surname and 123,057 with it as their second surname in census data dated 1 January 2025. The provincial rates for the first surname were especially high in A Coruña (11.342 per thousand), Lugo (10.763), Pontevedra (9.056), and Ourense (5.998); Córdoba also had a high rate (6.326). The INE's full Castro table shows that the surname is present across Spain rather than confined to Galicia.
This pattern is consistent with a strong northwestern association, but it is modern residence data, not a map of medieval origins. It cannot identify the home place of a Castro family now living in Madrid, Galicia, Andalusia, Portugal, Italy, or the Americas.
What the Surname Can—and Cannot—Tell You
For an individual family, the central question is not simply “Where does Castro come from?” but “Which Castro line is documented here?” Useful distinctions include:
- whether early records say Castro or de Castro;
- whether the family first appears in a Galician, Portuguese, other Spanish, Sephardic, or Italian setting;
- whether a nearby locality actually bears Castro as a simple or compound place-name; and
- whether successive records connect the generations, rather than merely repeating a common surname.
The etymology explains how the name could form. It does not establish ethnicity, nobility, a coat of arms, or kinship with a notable bearer.
References
- Patrick Hanks, Simon Lenarčič, and Peter McClure, eds., Dictionary of American Family Names, 2nd ed. (Oxford University Press, 2022), s.v. “Castro,” entry text reproduced by Ancestry.
- Patrick Hanks, Simon Lenarčič, and Peter McClure, eds., Dictionary of American Family Names, 2nd ed. (Oxford University Press, 2022), s.v. “De Castro,” entry text reproduced by Ancestry.
- Real Academia Española and Asociación de Academias de la Lengua Española, “castro,” *Diccionario de la lengua española*, 23rd ed., online entry.
- Real Academia Galega, “Castro,” *Guía de apelidos galegos*.
- Porto Editora, “Castro,” *Dicionário Infopédia de Toponímia*.
- Seminario de Onomástica da Real Academia Galega and Xunta de Galicia, “Informe sobre o cámbio do nome do concelho do Castro de Caldelas,” *Toponimia de Galicia*.
- Instituto Nacional de Estadística, “Frecuencias de apellidos: Castro”, Annual Population Census data at 1 January 2025.
- F. De Ruyt, “Castro,” *Enciclopedia dell'Arte Antica* (Treccani, 1973).