The organization received a boost in prestige when President Andrew Jackson invited his postmaster general, William T. Barry, to sit as a member of the Cabinet in 1829.

On February 17, 1691, a grant of letters patent from the joint sovereigns, William III and Mary II, empowered him: to erect, settle, and establish within the chief parts of their majesties' colonies and plantations in America, an office or offices for receiving and dispatching letters and pacquets, and to receive, send, and deliver the same under such rates and sums of money as the planters shall agree to give, and to hold and enjoy the same for the term of twenty-one years.

[4] The patent included the exclusive right to establish and collect a formal postal tax on official documents of all kinds.

Journalists took the lead, securing post office legislation that allowed them to reach their subscribers at very low cost, and to exchange news from newspapers between the thirteen states.

Before the Revolution, individuals like Benjamin Franklin and William Goddard were the colonial postmasters who managed the mails then and were the general architects of a postal system that started out as an alternative to the Crown Post.

The 1792 law provided for a greatly expanded postal network, and served editors by charging newspapers an extremely low rate.

Bruce Adamson wrote that: "Next to Benjamin Franklin, Rufus Easton was one of the most colorful people in United States Postal History."

In 1806 Postmaster General Gideon Granger wrote a three-page letter to Easton, begging him not to partake in a duel with vice-president Aaron Burr.

Easton, at Fort Union, New Mexico, had occasion to send some message east by a certain date, and contracted with Aubrey to carry it to the nearest post office (then Independence, Missouri), making his compensation conditional on the time consumed.

He was fortunate in meeting several outward-bound trains, and thereby made frequent changes of horses, some four or five, and reached Independence in six days, having hardly rested or slept the whole way.

"[9] To cover long distances, the Post Office used a hub-and-spoke system, with Washington as the hub and chief sorting center.

Letters from early settlers provided information and boosterism to encourage increased migration to the West, helped scattered families stay in touch and provide assistance, assisted entrepreneurs in finding business opportunities, and made possible regular commercial relationships between merchants in the west and wholesalers and factories back east.

The widespread circulation of important newspapers by mail, such as the New York Weekly Tribune, facilitated coordination among politicians in different states.

[14] Once it became clear that the postal system in the United States needed to expand across the entire country, the use of the railroad to transport the mail was instituted in 1832, on one line in Pennsylvania.

[16] An Act of Congress provided for the issuance of stamps on March 3, 1847, and the postmaster general immediately let a contract to the New York City engraving firm of Rawdon, Wright, Hatch, and Edson.

In 1855, William Henry Aspinwall completed the Panama Railway, providing rail service across the Isthmus and cutting to three weeks the transport time for the mails, passengers and goods to California.

[20] A bilateral parcel-post treaty between the independent (at the time) Kingdom of Hawaii and the USA was signed on December 19, 1888 and put into effect early in 1889.

While the Post Office agreed to deliver parcels sent into the country under the UPU treaty, it did not institute a domestic parcel-post service for another twenty-five years.

[22] The advent of Rural Free Delivery (RFD) in the U.S. in 1896, and the inauguration of a domestic parcel post service by Postmaster General Frank H. Hitchcock in 1913, greatly increased the volume of mail shipped nationwide, and motivated the development of more efficient postal transportation systems.

[23] Many rural customers took advantage of inexpensive Parcel Post rates to order goods and products from businesses located hundreds of miles away in distant cities for delivery by mail.

[24] In 1917, the Post Office imposed a maximum daily mailable limit of two hundred pounds per customer per day after a business entrepreneur, W. H. Coltharp, used inexpensive parcel-post rates to ship more than eighty thousand masonry bricks some four hundred seven miles via horse-drawn wagon and train for the construction of a bank building in Vernal, Utah.

[26][27] The advent of parcel post also led to the growth of mail order businesses that substantially increased rural access to modern goods over what was typically stocked in local general stores.

An Act of Congress of June 25, 1910, established the Postal Savings System in designated post offices, effective January 1, 1911.

Assistant Postmaster General Otto Praeger, appointed Benjamin B. Lipsner to head the civilian-operated Air Mail Service.

When the U.S. Congress passed the Comstock laws of 1873, it became illegal to send through the U.S. mail any material considered obscene or indecent, or which promoted abortion issues or birth control.

[36] On March 18, 1970, postal workers in New York City—upset over low wages and poor working conditions, and emboldened by the Civil Rights Movement—organized a strike against the United States government.

The act replaced the cabinet-level Post Office Department with a new federal agency, the United States Postal Service,[38] effective July 1, 1971.