In early 1916, Congress passed a law calling for the issuance of 100,000 gold dollars to be sold as souvenirs for $3 apiece to raise money for a memorial to the martyred President William McKinley in Niles, Ohio. Despite the lofty goals, only 20,026 pieces were struck in August and October 1916. The National McKinley Birthplace Memorial Association sold an estimated 8,000 pieces to the public, approximately 7,000 to Texas dealer B. Max Mehl (at reduced prices), and the rest were returned to the Mint and destroyed. Thus, the total number of 1916 McKinley Dollars that made it into the hands of the public is an estimated 15,000 pieces.
Virtually all of the known examples are Mint State, though a few "escaped" into circulation or were made into jewelry. As a result, the survival rate is extremely high. PCGS alone has certified over four thousand examples, the bulk of which grade out at MS64. Gems are common and even MS67 pieces are plentiful enough (but pricey).