Which metropolitan area had 21,436,911 residents in Mexico's 2020 census?

Greater Mexico City had 21,436,911 residents in Mexico’s 2020 census.

Greater Mexico City is the country’s largest metropolitan area, officially associated with the Metropolitan Area of the Valley of Mexico. It includes Mexico City itself and surrounding municipalities, especially in the State of Mexico, with the built-up region spreading across administrative boundaries. The 2020 figure therefore describes a metropolitan population, not the population of Mexico City’s city proper.

That distinction explains why other figures sometimes appear in references. Mexico City proper had about 9.2 million residents in the 2020 census, while the wider metropolitan area contained more than twice that number. Greater Guadalajara, Greater Monterrey, and Greater Puebla are also major Mexican metropolitan areas, but each had considerably fewer residents in 2020.

The region’s enormous scale reflects decades of urban expansion across the Valley of Mexico. Mexico City became the country’s political and economic center, while industrialization and migration enlarged its suburbs. Because metropolitan boundaries can be revised by Mexican authorities, later sources may publish different totals; the stated 21,436,911 is specifically the 2020-census figure used by this question.