The four states – Kentucky, Massachusetts, Pennsylvania, and Virginia – are all in the Eastern United States, and prior to the formation of the United States in 1776, were British colonial possessions (although Kentucky did not exist as an independent polity under British rule, instead being a part of Virginia). As such, they share a strong influence of English common law in some of their laws and institutions.
The term "commonwealth" does not describe or provide for any specific political status or legal relationship when used by a state. Those that do use it are equal to those that do not. A traditional English term for a political community founded for the common good, it is used symbolically to emphasize that these states have a "government based on the common consent of the people" as opposed to one legitimized through their earlier colonial status that was derived from the British crown. It refers to the common "wealth", or welfare, of the public and is derived from a loose translation of the Latin term res publica.
Criminal charges in these four states are brought in the name of the Commonwealth.
Besides the four aforementioned states, other states have also on occasion used the term commonwealth to refer to themselves:
Two U.S. territories are also designated as commonwealths: Puerto Rico and the Northern Mariana Islands. When used in connection with areas under U.S. sovereignty that are not states, the term broadly describes an area that is self-governing under a constitution of its own adoption and whose right of self-government will not be unilaterally withdrawn by the United States Congress.
On September 28, 1786, the residents of Kentucky County began petitioning the Virginia legislature for permission to become a "free and independent state, to be known by the name of the Commonwealth of Kentucky". On June 1, 1792, Kentucky County officially became a state. As in Virginia, the official title of the elected local prosecutor in each of Kentucky's political subdivisions is the Commonwealth's Attorney, as opposed to State's Attorney in other states or the more standard District Attorney. Kentucky is the only state outside of the original Thirteen Colonies that uses commonwealth in its name.