Washington Co., Wi – Thursday, December 8 is the Feast of the Immaculate Conception; it is a Holy Day of Obligation.
From catholicism.about.com:
Few doctrines of the Catholic Church are as misunderstood as the dogma of the Immaculate Conception of the Blessed Virgin Mary, which Catholics celebrate every year on December 8. Many people, including many Catholics, think that the Immaculate Conception refers to the conception of Christ through the action of the Holy Spirit in the womb of the Blessed Virgin Mary. That event, though, is celebrated at the feast of the Annunciation of the Lord (March 25, nine months before Christmas). What is the Immaculate Conception?
Conceived Without Sin
The Immaculate Conception refers to the condition that the Blessed Virgin Mary was free from Original Sin from the very moment of her conception in the womb of her mother, Saint Anne. We celebrate the Nativity of the Blessed Virgin Mary—her birth—on September 8; nine months before that is December 8, the Feast of the Immaculate Conception.