The 1918 Illinois Statehood Centennial ("Lincoln") Half Dollar was struck at the Philadelphia Mint in August 1918. The coin had an authorized mintage of 100,000, and all were struck in one batch (plus 58 coins for assay).
The Mint turned the coins around quickly, as they arrived in Springfield, Illinois by the end of the month. The Centennial Commission distributed the coins to designated banks in each Illinois County, with many receiving their coins and beginning local distribution in September.
The Centennial Commission, however, missed out on an ideal sales opportunity.
The 1918 Illinois State Fair and Centennial Exposition was scheduled to run through the middle of August (9th through 26th) and would have been an ideal venue for coin sales. Unfortunately, potential coin sale plans were thwarted when the 1918 Fair/Exposition was cancelled due to the Spanish Flu epidemic; the epidemic was a global crisis that is believed to have caused ~50 million deaths around the world. A temporary hospital to treat flu patients was opened on the Illinois State Fairgrounds in lieu of the Fair/Exposition.
The planned patriotic-themed Fair/Exposition was to include the former US President Theodore Roosevelt; he was invited to give an address during an August 26th special centennial program. Even though the Fair/Exposition was cancelled, Roosevelt still traveled to Springfield, IL (not the home of the Simpsons

) and delivered his speech on August 26, 1918. The speech included much about Germany, World War I and how the United States should have joined the war earlier than it did (the US entered WWI on April 6, 1917) vs. concentrating on Illinois.
Note: Why August 26th as a celebration date? Illinois achieved Statehood on December 3, 1818, but adopted its first Constitution (a necessary step before Statehood) on August 26, 1818.While it's impossible to say with certainty how many Illinois coins would have been sold at the Fair/Exposition, it seems safe to say sales would have lessened the amount of coins stored in Springfield banks and forgotten about until President Franklin Delano Roosevelt's declared 1933 "Bank Holiday." For more on the Illinois half dollar and the 1933 Bank Holiday, see:
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1918 Illinois Statehood Centennial - 1933 Bank Holiday1918 Illinois Statehood Centennial Half Dollar

For more of my topics on commemorative coins and medals, including more on the history and design of the Illinois half dollar discussed here, see:
Commems Collection.