When did Mexico City become Mexico D F?

Answer 1

From the Wikipedia:

"Independence for Mexico was declared by Agustin de Iturbide in 1821 after he and his army marched into the city. While Iturbide's regime tried to keep as much of the old order as possible, he soon had to abdicate and Mexico was declared a republic in 1824, with Mexico City as its capital. Unrest followed for the next several decades, as different factions fought for control of Mexico. The Mexican Federal District was established by the new government and by the signing of their new constitution, where the concept of a federal district was adapted from the American constitution. Before this designation, Mexico City had served as the seat of government for both the State of Mexico and the nation as a whole."

Answer 2

On November 18, 1824. As soon as Mexico became a federal republic, it required a federal district, which would be home to the three federal powers (executive, legislative, the judiciary). As Mexico City was already the largest city in Mexico, it was selected as the primary site for such political entity.