The state of Mexico is one of the 32 federal entities of Mexico, and is divided into 125 municipalities. The Mexican Political Constitution, in its article 115 establishes that "The States will adopt, for their internal regime, the republican form of government, representative, popular, having as base of its territorial division and of its political and administrative organization, the Free Municipality.»Each municipality has its own municipal seat, which serves as seat of the power of the municipal government, besides that, often, it is the most important locality in the territory.
Some of the municipalities of Mexico were founded since colonial times, when they were part of the Intendancy of Mexico, but most of them were founded between 1824 and 1875, when the multiple reforms to the territorial organization of the entities of the country. Several municipalities arose as a result of the demographic and economic growth of their territory, and the need to have the seat of the municipal government closer to other communities. Tonanitla, in the northeastern zone, is the youngest municipality of the state, since it was created in 2003, although there are still several territories that seek to obtain the title of municipality. In the decade of 1970, the National Institute of Statistics and Geography created a key for each federal entity and Mexican municipality, with the purpose of facilitating the obtaining of data and to speed up some calculations.
Since then, the list prepared by the institute has not been modified, which is evidenced in the obsolete alphabetical order it presents, and the fact that newly created municipalities were added to the end of the list. The table also serves to locate the municipality on the map below. Many of the names of the municipalities have a pre-Hispanic origin that comes from the Nahuatl language, only the name of Acambay comes from the Purépecha. Those with a name of Hispanic origin refer to illustrious figures of the state, national heroes and characters of the Catholic saints, Polotitlán is the only one that combines in one word a Spanish root and a Nahuatl root. The etymological origin of the name of a municipality is reflects in those symbols, glyphs and shields used to represent them.
In addition, by listing certain features of the natural landscape and human activities that are specific to each municipality, these shields and etymological representations have become an important element of municipal identity. Being the most populated entity in the country, the state of Mexico has eight municipalities that exceed half a million inhabitants. Ecatepec de Morelos, is the most populated municipality in the country with 1 656 107 inhabitants, and the less populated municipality of Mexico - Zacazonapan - exceeds 4000. On the contrary, none of the municipalities of Mexico exceeds 800 km², being Tlatlaya the largest municipality in the state, with an area of 791.49 km². For its part, with only 3.19 km², Papalotla is the smallest municipality in the state, and one of the smallest in the country.