In Philadelphia, on July 26, 1775, Benjamin Franklin was named the first Postmaster General of the newly established United States Post Office. He still held that office the following summer when the Declaration of Independence was drafted and signed, and, so, remained the Postmaster General of the United States Post Office (USPO) until Nov, 1776.
Then in 1792, as a result of the Postal Clause, the United States Post Office became the United States Post Office Department (USPOD) and congress was given the power to create post roads and post offices.
August of 1970, President Richard Nixon signed The Postal Reorganization Act and the USPOD became the United States Postal Service (USPS). The first clause of The Postal Reorganization Act reads:
“The United States Postal Service shall be operated as a basic and fundamental service provided to the people by the Government of the United States, authorized by the Constitution, created by Act of Congress, and supported by the people. The Postal Service shall have as its basic function the obligation to provide postal services to bind the Nation together through the personal, educational, literary, and business correspondence of the people. It shall provide prompt, reliable, and efficient services to patrons in all areas and shall render postal services to all communities. The costs of establishing and maintaining the Postal Service shall not be apportioned to impair the overall value of such service to the people.”