The Louisiana Purchase Exposition Issue publicized the 1904 World’s Fair, held in St. Louis, Missouri. Five single-color stamps in values of 1-cent, 2-cent, 3-cent, 5-cent, and 10-cent inscribed “Commemorative Series of 1904” were issued in conjunction with the fair's opening on April 30, 1904.
Three stamps feature men who were intimately involved in the Louisiana Purchase (1803): U.S. Ambassador to France Robert Livingston, Secretary of State James Monroe, and President Thomas Jefferson. The 1-cent stamp shows a map of the Louisiana Purchase, the first map to appear on a U.S. stamp. The subject of the 5-cent stamp depicts William McKinley, who had nothing to do with the Louisiana Purchase. He earned his place on the stamp because he was the president who signed the legislation giving federal sanction to the Exposition. This stamp essentially became a memorial to McKinley, who was assassinated in 1901.
Encyclopedia of United States Stamps and Stamp Collecting
May 16, 2006