Etymology

Mēxihco is the Nahuatl term for the heartland of the Aztec Empire, namely the Valley of Mexico and surrounding territories, with its people being known as the Mexica. The terms are plainly linked; it is generally believed that the toponym for the valley was the origin of the primary ethnonym for the Aztec Triple Alliance, but it may have been the other way around. In the colonial era, when Mexico was called New Spain, this central region became the Intendency of Mexico, during the eighteenth-century reorganization of the empire, the Bourbon Reforms. After the colony achieved independence from the Spanish Empire in 1821, said territory came to be known as the State of Mexico, with the new country being named after its capital: Mexico City, which itself was founded in 1524 on the site of the ancient Mexica capital of Mexico-Tenochtitlan.

The official name of the country has changed as the form of government has changed. The declaration of independence signed on 6 November 1813 by the deputies of the Congress of Anáhuac called the territory América Septentrional (Northern America) in the Plan of Iguala (1821). On two occasions (1821–1823 and 1863–1867), the country was known as Imperio Mexicano (Mexican Empire). All three federal constitutions (1824, 1857 and 1917, the current constitution) used the name Estados Unidos Mexicanos—or the variant Estados-Unidos Mexicanos, all of which have been translated as "United Mexican States". The phrase República Mexicana, "Mexican Republic", was used in the 1836 Constitutional Laws.