Has a human ever been mailed via the United States Postal Service?

Actually, yes. Shortly after parcel post was introduced in the early 1900s, several parents sent their small children though the mail. This was done with the help of sympathetic postal workers, most commonly over short distances in rural areas. And it was cost effective—in 1913, it cost just 15 cents to mail an 8-month-old baby to his grandmother.

Before you get any big ideas, though, know that the fun came to an end in 1920 when the postmaster general officially outlawed sending people through the mail. How lame.

A runaway slave, with help, mailed himself north.

No

Yes. Here is some background information I found on the web

One of the earliest tales of beating the mail system occurred in 1849 with the escape of Virginia slave Henry “Box” Brown. One night, Brown had a dream to “mail [himself] to a place where there are no slaves.” With $86 in hand, Brown enlisted the help of a local storekeeper to box him up with water and biscuits and send him north to freedom. James Miller McKim, a Philadelphia abolitionist, agreed to receive the box. The trip began on March 23. While the journey only lasted 27 hours, Brown’s box was passed from wagon to railroad to steamboat and back again. The box often ended up upside down, but Brown remained quiet enough to avoid discovery. On March 24, Brown arrived in Philadelphia and was released as a free man.

That wasn’t the only case of shipping people by mail. In 1914, 5-year-old May Pierstorff was sent from Grangeville, Idaho to visit her grandmother in Lewiston, Idaho. When it came time to buy tickets, Pierstorff’s parents discovered that sending their daughter through parcel post was cheaper than buying fare. Pierstorff, who weighed less than the 50-pound weight limit, was sent through the mail at the chicken rate. Before Pierstorff boarded the train, her parents clipped 53 cents to her coat and sent her on her way. Upon arrival in Lewiston, the postmaster personally delivered the young girl to her grandmother’s house. Six years later, the practice of shipping humans through parcel post became illegal.

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