Electoral regions of Mexico

The electoral regions (circunscripciones electorales) of Mexico are geographic areas composed of various states used for the election of the 200 proportional representation legislators to the Chamber of Deputies.

Mexico is split into five separate regions. Each of the five regions elects 40 deputies, who are selected according to party lists in the regions. To distinguish them from those elected in the 300 single-member constituencies, they are often referred to as "plurinominal deputies".^[1][2]

The electoral regions are divided to ensure a roughly equal distribution of population among the regions and may be modified by the National Electoral Institute. The distribution in use since 30 September 2005 was slightly reorganized for the 2024 general election.^[3]

In contrast, the 32 senators-at-large elected to the Senate by the principle of proportional representation are drawn from party lists covering the entire country; the electoral regions therefore play no role in Senate elections.

	Region	Seat	States (2005–2023)[4]	States (2024–)[5]	2006 population[6]
	First	Guadalajara, Jalisco	Baja California, Baja California Sur, Chihuahua, Durango, Jalisco, Nayarit, Sinaloa, Sonora	Baja California, Baja California Sur, Chihuahua, Durango, Jalisco, Nayarit, Sinaloa, Sonora	21,136,816
	Second	Monterrey, Nuevo León	Aguascalientes, Coahuila, Guanajuato, Nuevo León, Querétaro, San Luis Potosí, Tamaulipas, Zacatecas	Aguascalientes, Coahuila, Guanajuato, Nuevo León, San Luis Potosí, Tamaulipas, Zacatecas (Querétaro was moved to the fifth region)	21,417,106
	Third	Xalapa, Veracruz	Campeche, Chiapas, Oaxaca, Quintana Roo, Tabasco, Veracruz, Yucatán	Campeche, Chiapas, Oaxaca, Quintana Roo, Tabasco, Veracruz, Yucatán	20,945,125
	Fourth	Mexico City	Mexico City, Guerrero, Morelos, Puebla, Tlaxcala	Mexico City, Guerrero, Hidalgo, Morelos, Puebla, Tlaxcala (Hidalgo was added from the fifth region)	20,173,001
	Fifth	Toluca, State of Mexico	Colima, Hidalgo, State of Mexico, Michoacán	Colima, State of Mexico, Michoacán, Querétaro (Hidalgo was moved to the fourth region and Querétaro was added from the second region)	21,172,323

The first steps away from a system based solely on single-member districts were taken with the 1963 constitutional amendments that introduced "party deputies" (diputados de partido). Under this mechanism, parties winning more than 2.5% of the popular vote were awarded five party deputy seats, with an additional seat for each 0.5% above that figure, up to a maximum of 20. Any single-member seats the party in question might have won counted towards the 20-seat ceiling, and parties winning more than 20 single-member seats (in practical terms, only the then-hegemonic Institutional Revolutionary Party) were not eligible for the party deputy mechanism.^[7] Party deputies were first elected in the 1964 general election, in which three opposition parties – who collectively failed to win any first-past-the-post districts – were allocated 34 seats.^[8]

The electoral region mechanism was introduced as part of the 1977 political reforms.^[9] First used for the 1979 legislative election, there were at first only three regions, which elected 100 plurinominal deputies. For the 1982 general election, the number was increased to four, and the fifth region was introduced for the 1985 mid-terms. Following further reforms in 1986, the number of plurinominal seats in the Chamber was increased to 200 for the 1988 election.^[6]

• National Electoral Institute
• Chamber of Deputies (Mexico)
• Elections in Mexico