The Valley of Mexico, sometimes also called Basin of Mexico, is a highlands plateau in central Mexico. Surrounded by mountains and volcanoes, the Valley of Mexico was a centre for several pre-Columbian civilizations including Teotihuacan, the Toltec, and the Aztec Empire. The valley used to contain five interconnected lakes called Lake Zumpango, Lake Xaltocan, Lake Xochimilco, Lake Chalco and the largest, Lake Texcoco, covering about 1,500 square kilometers (580 sq mi) of the valley floor. When the Spaniards arrived in the Valley of Mexico, it had one of the highest population concentrations in the world with about one million people. After the conquest of the Aztec Empire, the Spaniards rebuilt the largest and most dominant city, Mēxihco Tenōchtitlan, renaming it Ciudad de México and over time began to drain the lakes' waters to control flooding.

The State of Mexico, officially just Mexico, is one of the 32 federal entities of the United Mexican States. Commonly known as Edomex to distinguish it from the name of the whole country, it is the most populous, as well as the most densely populated, state in the country.