Oddly, they were not added in chronological order. The stars for the Chicago Fire (1871) and the Columbian Expo (1893) were present on the first flag design in 1917, but the star for the Century of Progress was added during the year of the expo (1933), and the star for Fort Dearborn was added in 1939, 127 years after Fort Dearborn was destroyed (which itself was years after the fort was built).