The King's Highway was a roughly 1,300-mile (2,100 km) road laid out from 1650 to 1735 in the American colonies. It was built on the order of Charles II of England, who directed his colonial governors to link Charleston, South Carolina, and Boston, Massachusetts.

The section north of New York City, laid out on January 22, 1673, became the Upper Boston Post Road.^[1] The road was finally completed in 1735. Much of the Post Road is now U.S. Route 1 and U.S. Route 20.

The King's Highway Historic District in New Jersey covers U.S. Route 206 and New Jersey Route 27, connecting Lawrenceville with Kingston through Princeton.^[2]

In Pennsylvania, much of the route is now U.S. Route 13.^[3] (In Philadelphia, Route 13 becomes Frankford Avenue.)^[4]

Through Maryland, the King's Highway largely follows U.S. Route 1.^[5]

From Virginia southward, the modern U.S. 17 has many segments that follow the old King's Highway.

Herman Moll's 1729 "Post Map" described the route:

An Account of ye Post of ye Continent of Nth. America as they were Regulated by ye Postmasters Genl. of ye Post House. The Western Post setts out from Philadelphia every Fryday leaving Letters at Burlington and Pert Amboy and arrives at New York on Sunday night; the distance between Philadelphia & New York being 106 Miles. The Post goes out Eastward every Monday morning from New York, and arrives at Seabrook Thursday noon; being 150 Miles, where the Post from Boston setts out at the same time: the New York Post returning with the Eastern Letters, and the Boston Post with the Western, Bags are dropt at New London, Stommington, Rhode Island, and Bristol. The Post from Boston to Pisacataway being 70 Miles leaves Letters at Ipswich, Salem, Marblehead and Newberry. There are offices kept at Burlington, Perth Amboy in New Jersey, New London and Stommington in Connecticott, at Rhode Island, Bristol, Ipswich, Salem, Marblehead and Newberry. and the 3 Great Offices are at Boston, New York, & Philadelphia.^[6]

The Boston Post Road was a system of mail-delivery routes between New York City and Boston that evolved into the first major highways in the United States. Some routes followed trails in use by Native Americans long before Europeans arrived. Some of these important native trails had been used long enough that they were two feet below the surrounding woodland.^[7]

Following a trail known as the Pequot Path, the Upper Post Road was first laid out on January 1, 1673.^[8] Used by post riders to deliver the mail, it was later widened and smoothed so that horse-drawn wagons or stagecoaches could use it. During the 19th century, turnpike companies took over and improved pieces of the road. Large sections of the various routes are still called the King's Highway and Boston Post Road.

In 1761, then-Postmaster General Benjamin Franklin ordered milestones placed along the 1673-established route from Boston to Saco, Maine, initially, then all the way to Machias, as a northern extension of King's Highway.^[9][10]

As part of his duties, Franklin conducted inspections of the roads that were used for delivering mail as settlements along the coast increased.^[11] One method of charging for mail service was by mileage, so Franklin invented an odometer to measure mileage more accurately. The King's Highway, as a result, morphed into the Post Road.^[12]

• The Post Road in New York
• Milestone 8 on the Upper Post Road in Harvard Square

• List of roads and highways
• Washington-Rochambeau Revolutionary Route
• Assunpink Trail
• King's Highway Historic District