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El Chichón is the only active volcano within the Chiapanecan Volcanic Arc, Southern Mexico, which is located between the Trans-Mexican Volcanic Belt and the Central America Volcanic Arc. Remote sensing, fieldwork, geochronology, and petrology studies have shown that at least 11 eruptions have occurred in El Chichón within the last 8000 years, forming a complex of lava domes with a central crater and surrounding pyroclastic deposits. This paper contributes to a new understanding of El Chichón’s eruptive history and magmatic evolution through dating crystallization ages of zircon, which originate within the intrusive complex underneath the volcano. Zircon dating focused on the most recent eruption of 1982 and the antecedent AD 1450 eruption. U-Th disequilibrium zircon ages range from 9.3±2.7 ka to 734+∞/-511 ka in composite pumice samples from a pyroclastic flow and lava from an intracrater dome (errors 1σ; ∞ indicating secular equilibrium). Overlapping U-Th zircon ages between 5.8+4.7/-4.5 ka and secular equilibrium were obtained for a composite pumice sample from the AD 1450 eruption. Because many older ages overlap within uncertainty with secular equilibrium for 230Th/238U, reconnaissance U-Pb dating was performed of the same crystals. The U-Pb ages range between ca. 290 Ma and 1.2 Ga and indicate xenocrystic origins for these crystal domains. This is the first evidence for zircon recycling from crustal rocks, and the generation of young zircon crystals and overgrowths in a long-lived magma system underneath El Chichón. This new application of zircon dating for El Chichón determines ages of zircon crystallization in a subterranean magma reservoir, which significantly predates what is recorded in eruptive stratigraphy.