People in Mexico and in the United States celebrate the Feast of Our Lady of Guadalupe on December 12. Mary is the Patron Saint of Mexico and Patroness of the Americas. Every year, thousands of people from all over the country make a pilgrimage to the Basilica in Mexico City. The day commemorates her apparition to Saint Juan Diego in the hills of Tepeyac in 1531. She asked him to go to the bishop and tell him that the Ever Virgin Mary, Mother of God, sent him to ask for a church to be built atop Tepeyac hill.
Sourced from http://saintsresource.com/our-lady-of-guadalupe