History of United States postage rates

The system for mail delivery in the United States has developed with the nation. Rates were based on the distance between sender and receiver in the nation's early years. In the middle of the 19th century, rates stabilized at one price regardless of distance. Rates were relatively unchanged until 1968 when the price was increased every few years by a small amount. Comparing the increases with a price index, the cost of a first-class stamp has been steady. The seal of the Post Office Department showed a man on a running horse, even as railroads and, later, motorized trucks and airplanes moved mail. In 1971, the Post Office became the United States Postal Service, with rates set by the Postal Regulatory Commission, with some oversight by Congress. Air mail became standard in 1975. In the 21st century, prices were segmented to match the sorting machinery used; non-standard letters required slightly higher postage.