I found an official site for the gov't. of MA; their governor's first name is Mitt! I wonder if this link is an intentional redundancy:
Find public hearings, recreational events and more.
These four are commonwealths, not states: Kentucky, Massachusetts, Pennsylvania, and Virginia. Here's a quote from a site that says something similar to what I found before:
WE CONTACTED ERIC USLANER, PROFESSOR OF GOVERNMENT AND POLITICS AT THE UNIVERSITY OF MARYLAND FOR YOUR ANSWERS. THE PROFESSOR SAYS THERE IS NO DIFFERENCE BETWEEN A STATE AND COMMONWEALTH.

THE ENGLISH STARTED USING THE TERM COMMONWEALTH IN THE MIDDLE OF THE 17TH CENTURY. VIRGINIA, PENNSYLVANIA, MASSACHUSETTS AND KENTUCKY ALL USE THE TERM COMMONWEALTH, WHICH ACTUALLY MEANS GOVERNMENT FOR THE COMMON GOOD. IT CAN ALSO REFER TO A TERRITORY SUCH AS PUERTO RICO.