El Oro is one of 125 municipalities in the State of Mexico within the United Mexican States. The municipal seat is the town of El Oro de Hidalgo. The name El Oro means "the gold" in Spanish. It has subsequently been given an alternative Nahuatl name of "Teocuitlatl", meaning "sacred excrement". Its seal, in the form of an Aztec glyph, contains elements referring to gold and to caves, of which there are many in the municipality.