Official Holidays:

January 1 New Year's Day

February 5

Constitution Day
March 21 Benito Juarez's Birthday
May 1 Labor Day
September 16 Mexican Independence Day
November 20 Revolution Day
December 25 Christma's Day

Non obligatory holidays wich are often taken by banks and many companies are:

January 6

Three King's Day(Mexican children receive Christmas gifts)

February 24 Flag Day
April 30 Children's Day
May 5 Battle of Puebla(in this battle Mexican forces defeated the French interventionist army wich later won and placed Maximiliian and Carlota as emperors of Mexico)
May 10 Mother's Day
May 15 Teacher's Day
September 1 State of the Union Adress
October 12 Columbu's Day(Dia de la Raza)
November 2 Day of the Dead(This is one of the most important religious holidays as it is the day in wich people go to the cementery to honor thier dead.)
December 12 Day of the Virgin of Guadalupe(She is the patron saint of Mexico and people make pilgimages form all over the country to the Basilica of Guadalupe in Mexico City to pray homage.)
December 16 The Chistmas Posadas begin

Consult the tourist office to find out aobut holidays in the region you'll be visiting. Keep in mind that there are 175 additional holidays in Mexico, most of them religious. Be consider to show respect for these celebrations. Don't drive your car through a procession.