The United States dollar (USD) is the official currency of the United States and its territories per the Coinage Act of 1792. One dollar is divided into 100 cents, or into 1000 mills for accounting and taxing purposes. The Coinage Act of 1792 created a decimal currency by creating the dime, nickel, and penny coins, as well as the dollar, half dollar, and quarter dollar coins, all of which are still minted in 2020.

Several forms of paper money were introduced by Congress over the years, the latest of which being the Federal Reserve Note that was authorized by the Federal Reserve Act of 1913. While all existing U.S. currency remains legal tender, issuance of the previous form of the currency (U.S. notes) was discontinued in January 1971. As a result, paper money that is in current circulation consists primarily of Federal Reserve Notes that are denominated in U.S. dollars.

More Info: en.wikipedia.org