Today, four mints operate in the United States producing billions of coins each year. The main mint is the Philadelphia Mint, which produces circulating coinage, mint sets and some commemorative coins. The Denver Mint also produces circulating coinage, mint sets and commemoratives. The San Francisco Mint produces regular and silver proof coinage, and produced circulating coinage until the 1970s. The West Point Mint produces bullion coinage (including proofs). Philadelphia and Denver produce the dies used at all of the mints. The proof and mint sets are manufactured each year and contain examples of all of the year's circulating coins.
The producing mint of each coin may be easily identified, as most coins bear a mint mark. The identifying letter of the mint can be found on the front side of most coins, and is often placed near the year. Unmarked coins are issued by the Philadelphia mint. Among marked coins, Philadelphia coins bear a letter P. Denver coins bear a letter D, San Francisco coins bear a letter S, and West Point coins bear a letter W. S and W coins are rarely, if ever, found in general circulation, although S coins bearing dates prior to the mid-1970s are in circulation. The CC, O, C, and D mint marks were used on gold and silver coins for various periods in the mid-nineteenth century until the early twentieth century by temporary mints in Carson City, Nevada; New Orleans, Louisiana; Charlotte, North Carolina; and Dahlonega, Georgia; respectively: most such coins still extant are now in the hands of collectors and museums.
Non-circulating bullion coins have been produced each year since 1986. They can be found in silver, gold and also platinum since 1997. Recently, the mint introduced palladium bullion too. The face value of these coins is legal as tender, but does not actually reflect the value of the precious metal contained therein. On May 11, 2011, Utah became the first state to accept these coins as the value of the precious metal in common transactions. The Utah State Treasurer assigns a numerical precious metal value to these coins each week based on the spot metal prices.
Note: It is a common misconception that "eagle"-based nomenclature for gold U.S. coinage was merely slang. This is not the case. The "eagle," "half-eagle" and "quarter-eagle" were specifically given these names in the Coinage Act of 1792. Likewise, the double eagle was specifically created as such by name ("An Act to authorize the Coinage of Gold Dollars and Double Eagles", title and section 1, March 3, 1849).