Some numismatists consider the denomination to be the first coin minted by the United States Mint under the Coinage Act of 1792, with production beginning on or about July 1792. However, others consider the 1792 half dime to be nothing more than a pattern coin, or 'test piece', and this matter continues to be subject to debate.
These coins were much smaller than dimes in diameter and thickness, appearing to be "half dimes".
In the 1860s, powerful nickel interests successfully lobbied for the creation of new coins, which would be made of a copper-nickel alloy; production of such coins began in 1865, and were struck in two denominations — three and five cents (the latter introduced in 1866).
The introduction of the copper-nickel five-cent pieces made the silver coins of the same denomination redundant, and they were discontinued in 1873.
1792 Half Dime
The half dime was one of the early coins of the U.S. Mint. Authorized by the Act of April 2, 1792, it lasted until 1873. Until 1829 it showed no value anywhere on its obverse or reverse.
Flowing Hair 1794–1795
The flowing hair half dime was designed by Robert Scot and this same design was also used for half dollar and dollar silver coins minted during the same period. The obverse bears a Liberty portrait similar to that appearing on the 1794 half cent and cent but without the liberty cap and pole. Mintage of the 1794 version was 7,765 while 78,660 of the 1795 version were produced.
Draped Bust (Small Eagle Reverse) 1796–1797
The obverse of the draped bust half dime was based on a sketch by artist Gilbert Stuart, with the dies engraved by Robert Scot and John Eckstein. The primary 1796 variety bears fifteen stars representing the then number of states in the union. In 1797, fifteen and sixteen star varieties were produced – the sixteenth star representing newly admitted Tennessee – as well as a thirteen star variety after the mint realized that it could not continue to add more stars as additional states joined the union. The reverse bears an open wreath surrounding a small eagle perched on a cloud. 54,757 half dimes of this design were minted.
Draped Bust (Heraldic Eagle Reverse) 1800–1805
Following a two-year hiatus, mintage of half dimes resumed in 1800. The obverse remained essentially the same as the prior version, but the reverse was revised substantially. The eagle on the reverse now had outstretched wings, heraldic style. This reverse design first appeared on gold quarter and half eagles and then dimes and dollars in the 1790s. Mintage of the series never surpassed 40,000, with none produced in 1804. No denomination or mintmark appears on the coins; all were minted in Philadelphia.
Capped Bust 1829–1837
Production of half dimes resumed in 1829 based on a new design by Chief Engraver William Kneass, who is believed to have adapted an earlier John Reich design. All coins were minted at Philadelphia and display no mintmark. The high circulating mintage in the series was in 1835, when 2,760,000 were struck, and the low of 871,000 was in 1837. Both Capped Bust and Liberty Seated half dimes were minted in 1837.
Seated Liberty (various subtypes) 1837–1873
The Seated Liberty series is divided into several subtypes. The first was struck at Philadelphia in 1837 and New Orleans in 1838 and lacks stars on the obverse. In 1838 a semicircle of 13 stars was added around the obverse border, and this basic design was used through 1859. In 1853, small arrows were added to each side of the date to reflect a reduction in weight due to rising silver prices, and the arrows remained in place through 1855. The arrows were dropped in 1856, with the earlier design resumed through 1859. In 1860, the obverse stars were replaced with the inscription UNITED STATES OF AMERICA and the reverse wreath was enlarged. This design stayed in place through the end of the series. In 1978 a unique 1870-S Seated Liberty half dime became known. The Seated Liberty half dime was produced at the Philadelphia, San Francisco and New Orleans mints in an aggregate amount of 84,828,478 coins struck for circulation.  See also United States Seated Liberty coinage.
1870-S half dime
In 1978 a coin collector surprised the coin collecting community with an 1870–S (San Francisco) half dime, believed to have been found in a dealer's box of cheap coins at a coin show. According to mint records for 1870, no half dimes had been minted in San Francisco; yet it was a genuine 1870-S half dime. At an auction later that same year, the 1870-S half dime sold for $425,000. It is believed that another example may exist—along with other denominations minted that year in San Francisco—in the cornerstone of the old San Francisco Mint. Later in July, 2004, the discovery coin sold for $661,250 in MS-63 in a Stack`s-Bowers auction.