Within the US Treasury Department, the US Mint produces all circulating US coins. It not only issues the four coin denominations currently in circulation (pennies, nickels, dimes, and quarters), but also medals of honor, collector-focused coins (like the half-dollar and $1 coin, which can also be accepted as legal tender), and more. Notably, it doesn’t produce paper money; the Bureau of Engraving and Printing handles that.
The US Mint was created in 1792 after Congress passed the Coinage Act. Today, to get its coins into circulation, the US Mint works with the Federal Reserve, which distributes the new currency to Reserve Banks. The Reserve Banks then distribute those coins to depository institutions (think: commercial banks).
To combat counterfeiting, the US Mint implements security features into the designs of its coins. Any US coin that the Treasury no longer makes is still considered viable United States currency.