"A feast called the Conception of Mary arose in the Eastern Church in the seventh century. It came to the West in the eighth century. In the 11th century it received its present name, the Immaculate Conception. In the 18th century it became a feast of the universal Church. It is now recognized as a solemnity.
In 1854, Pius IX solemnly proclaimed: 'The most Blessed Virgin Mary, in the first instant of her conception, by a singular grace and privilege granted by almighty God, in view of the merits of Jesus Christ, the savior of the human race, was preserved free from all stain of original sin.' ..."
Click on the following link from franciscanmedia to read more about the Immaculate Conception of Mary: https://www.franciscanmedia.org/saint-of-the-day/immaculate-conception-of-the-blessed-virgin-mary