Catholics started to visit the shrine on River Road on Sunday for the woman they consider the blessed mother. The first official mass started Monday night and will continue every couple hours into the night and Tuesday until 7 p.m.
The Des Plaines shrine is the only place in the United States where the believers can offer prayers and leave flowers for Our Lady of Guadalupe, or the Virgin Mary.
More than 300,000 pilgrims are expected to make the holy pilgrimage by Tuesday, when the shrine will be covered with thousands of bouquets of flowers and lit up with hundreds of votive candles.
Many pilgrims will walk dozens of miles or more, a sacrifice they willingly make for their faith.
"We witness the extremes people will go to show that faith," Fr. Esequiel Sanchez, the church rector.
In some cases, the pilgrims come to pray and ask for help. Others want to say "thank you" for prayers they believe were answered.
Hilda Ramirez, who visited the shrine on Monday, is grateful because she believes her prayers for her 8-year-old son, who had Stage 4 cancer, were answered, despite the prognosis from doctors.
"(He had) zero chances of surviving. ... And thanks to her, he's still here," Ramirez said.
It was four years ago when doctors told her to just "give him quality of life because he wasn't going to make it," Ramirez said.
The third grader has been through about 40 surgeries to try to remove malignant tumors.
"We've been through hell but thanks to her and God, he's still here living with us," she said.
"THEY REALLY BELIEVE"
Ramirez is typical of a number of pilgrims who pray to the Virgin Mary and come to the shrine on her feast day on Dec. 12 each year.
"That's an indescribable experience, you'll see tears everywhere because they really believe," Sanchez said.
The Des Plaines shrine is one of only two for the Virgin Mary that is endorsed by the Catholic church.
The other is outside of a basilica in Mexico City, which is why pilgrims come from all over to show their faith.