U.S. Mail Railway Post Offices in Illinois.

Soon after railroads appeared in the 1830s, they started moving the U.S. mail. During the Civil War, railroads built rolling post offices to sort mail along the route besides moving mail. Special railroad cars called Railway Post Offices (RPO) employed postal workers to sort and handle mail in transit. They would pick up and drop off mail at station stops. They would pick up mail on the fly at places they didn't stop, "grabbing" mailbags from a special bracket without stopping the train. 

Mail Bag Catch & Drop from a Steam Locomotive Train.

Some electric interurban routes also had RPOs, which served the same functions as RPOs on steam (and later diesel) railroads. People could deposit mail on these cars via slots on their sides, and clerks would postmark that mail on board.

Illinois Central's United States Mail Railway Post Office № 51.

At their peak in the 1800s, RPO cars were used on over 9,000 train routes. But in the 20th Century, RPO use started to decline. After WWII, the Post Office began using large regional centers with machines taking over the sorting. In 1948 the RPO network had shrunk to 794 lines. As the Post Office canceled their "mail by rail" contracts, passenger trains that relied on mail revenue lost that revenue, contributing to the eventual creation of Amtrak in 1971. 

United States Mail Railway Post Office - HO Scale Car. (1:87 scale = 3.5 mm to 1 foot)

On June 30, 1977, the last RPO ended operations after 113 years.

Compiled by Dr. Neil Gale, Ph.D.