Many people use common wealth and state interchangeably. This is acceptable since there is no significant difference between a state and a commonwealth. Some people may prefer to use the word state while others prefer to use the word commonwealth.
What is a Commonwealth
There really is not difference between a state and a commonwealth, with no special status or provision within a constitution for a commonwealth. States within the United States that choose to be called commonwealths do so for the history and their roots which they are immensely proud.
What is a State
The definition of a state is a small political territory that is made to make the governing of the country that the state belongs to easier. The United States are made up of states within a federation.
In this case, the federation did not divide the United States into states for governing purposes but rather it brought the states together that were already formed.
Each state has its own government and then there is a federal government that governs the states.
When the United States was founded, the term commonwealth was used to describe a region that was governed by the people instead of a monarch.
During the American Revolution, Massachusetts, Pennsylvania and Virginia were declared to be commonwealths. This was their way of saying that they were no longer to be governed by the British crown.
As more states joined the union following the American Revolution, instead of calling themselves commonwealths, they started being referred to as states since they were never under British rule as a colony or commonwealth.
The Difference is in the Name
Commonwealth and state is only in the name with regard to the United States, some states chose to still call themselves commonwealths instead of states, but in reality, they are still a state.
There are 50 states that make up the United States and of these 50 states, there are four that choose to still be called commonwealths: Massachusetts, Virginia, Pennsylvania and Kentucky.
Commonwealth when used in other countries is often used to refer to countries that were at one time ruled by England and were at one time part of the British Empire. Also know the difference between Great Britain and UK.