Sister Faustina Kowalska was a Polish nun in Krakow, Poland. In 1931 Jesus appeared to her and spoke to her about Divine Mercy and asked her to paint an image of Him that we recognize today as Divine Mercy. Faustina was canonized a Saint on April 30, 2000. Her feast day is October 5th.
He stated: “I want the image solemnly blessed on the first Sunday after Easter, and I want it to be venerated publicly so that every soul may know about it“.
The Feast of Divine Mercy had been celebrated in Poland and in Vatican City, but on April 30, 2000, the Second Sunday of Easter was officially pronounced as Divine Mercy Sunday to be celebrated worldwide. Saint John Paul II later instituted a plenary indulgence for those who participate in the devotion and, in fact, St. John Paul II was canonized on the feast of Divine Mercy in 2014.
Jesus also told her: I want to grant a complete pardon to the souls that will go to Confession and receive Holy Communion on the Feast of My Mercy (1109). The soul that will go to Confession and receive Holy Communion will obtain complete forgiveness of sins and punishment.
People also are encouraged to pray the Novena of Divine Mercy, which begins Good Friday and ends the Saturday before Divine Mercy Sunday; to pray the Divine Mercy chaplet; and to be merciful toward others through words, actions and prayers. (To learn how to pray the Divine Mercy chaplet and novena, visit this page.)
The Shrine of Divine Mercy is located Krakow, Poland. Here is where she lived the latter part of her life and here is her tomb.
However, you can find the original image (shown here) is actually in Vilnius, Lithuania. Vilnius is where Saint Faustina spent a large part of her life and where she dictated the details of the image as given to her by Jesus.
In the U.S.A. you will find two shrines devoted to Divine Mercy, both in Massachusetts: