The first mail delivered by the Pony Express took 10 days from St. Joseph, Missouri to Sacramento, California.

Timeline

1803: Louisiana Purchase doubles the size of the United States.

1823: Congress designates all navigable waters (rivers and canals) be post roads.

1832: First mail is carried by train.

1838: Congress designates all railroads as post roads.

1845: Congress creates star routes.  This allows contractors, like stagecoach and Pony Express companies, to move the mail.

1846: The U.S. acquires the Oregon Territory.

1847: U.S. postage stamps issued meaning payment to mail a letter could be made by the sender.

1848: The U.S. acquires California and additional territories from Mexican Cession.

1848: Gold discovered in California.

1855: Pre-payment of mail became required, meaning payment to mail a letter had to be made by the sender.

1860: Pony Express Service started bringing mail between California and Missouri.  It lasted 18 months.

1861: The American Civil War begins.

1863: Postage rates become uniform, regardless of distance.

1864: Railway mail service begins; for the first time, mail is sorted on-board the train.

1867: The U.S. acquires the Alaskan Territory.

1869: Cross-country railroad completed; now mail can travel from coast to coast in 3 days.