Mexico has no official religion, actually, on the Constitution of 1917 several articles were written to impose limitations on the church. The governement does not provide any financial contributions to the church, and the church does not participate in public education. However, Christmas is a national holiday and every year during Easter and Christmas all schools in Mexico, public and private, send their students on vacation.
Despite this fact, the main religion in Mexico is the Catholic religion, and it is to be expected, after all, one of the Fathers of the Independence in Mexico was no other than a Priest, Miguel Hidalgo y Costilla gathered a lot of people on his little church in the town of Guadalupe and declared “el Grito de Independencia” a “warcry for arms and Independence under the flag of La Virgen de Guadalupe (one of the most famous Marian apparitions worldwide)”
This was probably one of the most decisive facts in Mexico religion and their turning to Catholicism, Father Miguel Hidalgo was, however, excommunicated from the Catholic church after this act.
In 1992, Mexico lifted almost all restrictions on the religions, including granting all religious groups legal status, conceding them limited property rights, and lifting restrictions on the number of priests in the country.
According to the last census, Roman Catholics are 88%of the total population, 47% percent of whom attend church services weekly, one of the lowest of the developing world. In absolute terms, Mexico has the world's second largest number of Catholics after Brazil, I guess you could call this Mexico religion.
Our Lady of Guadalupe, one of the world’s most famous Marian apparitions it is also considered a national symbol of Mexico.