Questions like these are typical. In the New York Times, William Safire answered this question.
Benjamin Franklin used the moniker United Colonies of North America during the 1775 battle for independence from Britain, according to his report. The Declaration of Independence adopted on July 4, 1776, had another name. The proclamation called the US.
The readers of Mr. Safire sent him further information. He discovered that two letters a month before the Declaration used the moniker United States of America. One appeared in the Pennsylvania Evening Post on June 29, 1776.
Ronald Gephart, a historian, spoke to Mr. Safire. Between 1774 and 1789, he searched Continental Congress delegates' communications. What he found. Richard Henry Lee of Virginia proposed before Congress on June 7, 1776, that the United Colonies be free and independent.
This plan created three committees to write three crucial texts. A Declaration of Independence was written. Others drafted Articles of Confederation. The third planned a pact. Three groups collaborated under the US designation.
Mr. Gephart stated the word came from committee members during these discussions. Also, the Articles of Confederation said, "The name of this confederation shall be the United States of America."