The indigenous language that's spoken by the largest group of people by far is Náhuatl, with over two and a half million speakers. Náhuatl is the language spoken by the Mexica (pronounced meh-shee-ka) people, who are also sometimes referred to as Aztecs, who live mainly in the central part of Mexico. The second-most-spoken indigenous language is Maya, with about one and a half million speakers. The Maya live in Chiapas and the Yucatan Peninsula.
Data from CDI, Comisión Nacional para el Desarrollo de los Pueblos Indígenas