The U.S. Mint in Denver produced double-headed Kennedy half-dollars in 1966, continuing a pattern first produced in 1964. Only coins minted in August, September, October, November or December 1966 are dated as 1966, with coins from earlier in the year retaining the 1965 stamp.
No proofs for the double-headed Kennedy half-dollar were struck in 1965, 1966 or 1967. While coins minted in 1964 contained a 90-percent silver alloy, those made in 1965 and after contained a lower amount of silver in favor of more copper and nickel. As of 2014, the U.S. Mint continues to manufacture the double-headed Kennedy half-dollar.