Organizers shifted the parade to the earlier date to avoid conflicting with Palm Sunday, the beginning of Holy Week, the Chicago Sun-Times reported Friday.
"This neighborhood is so heavily Catholic, it would just be inappropriate to have a parade on a day that is so religiously significant," said Mary Beth Sheehan, a parade committee member.
The U.S. Conference of Catholic Bishops said liturgical celebrations of St. Patrick's Day should be March 14, not March 17, because of Holy Week. March 15 was given to St. Joseph's Day, which is March 19, also in Holy Week this year.
St. Patrick's Day isn't a day Catholics must celebrate, Sister Mary Ann Walsh, spokeswoman for the U.S. Conference of Catholic Bishops, told the Sun-Times.
"It's a minor feast," she said. "Don't tell that to the Irish, though."