The Penny Post is any one of several postal systems in which normal letters could be sent for one penny

Penny

A penny is a coin or a type of currency used in several English-speaking countries. It is often the smallest denomination within a currency system.-Etymology:...

.
In England

Kingdom of England

The Kingdom of England was, from 927 to 1707, a sovereign state to the northwest of continental Europe. At its height, the Kingdom of England spanned the southern two-thirds of the island of Great Britain and several smaller outlying islands; what today comprises the legal jurisdiction of England...

, the Post Office had a monopoly on the collection and carriage of letters between post towns but there was no delivery system until the London Penny Post

London Penny Post

The London Penny Post was a premier postal system whose function was to deliver mail within London and its immediate suburbs for the modest sum of one penny. The Penny Post was established in 1680 by William Dockwra and his business partner, Robert Murray...

was established in 1680 by William Dockwra

William Dockwra

William Dockwra was an English merchant who along with his partner Robert Murry created the first Penny Post in London in 1680. In latter 17th century London there was no official postal system for mail delivery within the city of London and its suburbs. Dockwra's London Penny Post was a mail...

, and his partner Robert Murray. They established a local post

Local post

A local post is a mail service that operates only within a limited geographical area, typically a city or a single transportation route. Historically, some local posts have been operated by governments, while others, known as private local posts have been for-profit companies...

 that used a uniform rate of one old penny

Pound sterling

The pound sterling , commonly called the pound, is the official currency of the United Kingdom, its Crown Dependencies and the British Overseas Territories of South Georgia and the South Sandwich Islands, British Antarctic Territory and Tristan da Cunha. It is subdivided into 100 pence...

 for delivery of letters and packets up to one pound

Pound (mass)

The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...

 within the cities of Westminster and London

London

London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

 as well as Southwark.