In Poland, pączki are eaten especially on Fat Thursday (Tłusty Czwartek), the last Thursday prior to Ash Wednesday and the beginning of Lent. The traditional reason for making pączki was to use up all the lard, sugar, eggs and fruit in the house before Lent.
In North America, particularly the large Polish community of Chicago, Detroit, and other large cities across the Midwest, Paczki Day is celebrated annually by immigrants and locals alike. The date of this observance merges with that of pre-Lenten traditions of other immigrants (e.g., Pancake Day, Mardi Gras) on Fat Tuesday. With its sizable Polish population, Chicago celebrates the festival on both Fat Thursday and Fat Tuesday; pączki are also often eaten on Casimir Pulaski Day. In Buffalo, Toledo, Cleveland, Detroit, Grand Rapids, Milwaukee, South Bend, and Windsor, Pączki Day is celebrated on Fat Tuesday.