Which US coin type (as in Quarters, Cents, Dimes, Nickels, Half Dollars, etc.) has the most old coins out of all in circulation?
Randall Munroe, in his What If? article All the Money, claims that of all the coins in the world, there exists more of the U.S. penny than any other coin. His estimate of about 150 billion pennies currently in circulation is based on a 1996 General Accounting Office report on the future of the penny that cites a U.S. Mint estimate of 132 billion pennies in 1996, as well as the annual production numbers of the Mint.