For America250, on what date did Congress officially rename the union of colonies the United States?

Congress officially renamed the union of colonies the United States on September 9, 1776.

Before that date, congressional documents commonly used “United Colonies” for the revolutionary alliance. On September 9, Congress approved a change in its formal wording, replacing “United Colonies” with “United States.” The new name reflected the political transformation that followed the declaration of independence.

The change is easy to miss because the phrase “United States of America” already appeared in the Declaration of Independence, which Congress adopted in July. The September action was a separate administrative and political decision that standardized the name in official congressional documents. It did not create a new constitution or settle the structure of the national government.

The Articles of Confederation later provided the first written framework for the new union, but they were not finally ratified until 1781. America250 therefore looks back not only to the declaration itself, but also to the gradual development of the country’s name, institutions, and national identity during the Revolutionary War.