The Solemnity of the Immaculate Conception of the Blessed Virgin Mary is Friday, December 8, 2017. It is a holy day of obligation. Please check with your parish for Mass times (you can search for parishes around the diocese here).
On this day, we commemorate that from the moment of her conception, the Blessed Virgin Mary was in a state of grace and free from all original sin. The Solemnity of the Immaculate Conception is also the patronal feast day of the United States of America.