On 8th of August 1786 the US Congress unanimously chose the dollar as the unit of currency for the United States.
What currency shall we use?
With the declaration of Independence, the US Congress issued paper money, ‘Continental’ currency which eventually failed but at the same time the Spanish silver dollar was also being widely used.
By issuing the Declaration of Independence, adopted by the Continental Congress on July 4, 1776, the 13 American colonies severed their political connections to Great Britain. The Declaration summarized the colonists’ motivations for seeking independence. By declaring themselves an independent nation, the American colonists were able to confirm an official alliance with the Government of France and obtain French assistance in the war against Great Britain.Milestones: 1776
The issue of the Declaration was an important step in the recognition the US desired from other nations across the world.
The unanimous Declaration of the thirteen united States of America, When in the Course of human events, it becomes necessary for one people to dissolve the political bands which have connected them with another, and to assume among the powers of the earth, the separate and equal station to which the Laws of Nature and of Nature’s God entitle them, a decent respect to the opinions of mankind requires that they should declare the causes which impel them to the separation.Declaration of Independence: A Transcription
People in the American colonies prior to and after independence had been mostly using the Spanish silver dollar.
Then in 1792 the Coinage Act established the US dollar as the official currency and established the US Mint.