The Massachusetts Office of Coastal Zone Management limits its definition of the South Shore to the municipalities between Boston Harbor and Cape Cod which include Atlantic coastal and coastal watershed areas "from the three-mile limit of the state territorial sea to 100 feet beyond the first major land transportation route encountered (a road, highway, rail line, etc.)." 
For more information, click here. 

According to the Massachusetts Coastal Zone Management, there are 11 communities that make up the South Shore - in addition to the 6 listed above, the remaining towns include Duxbury, Hanover, Kingston, Pembroke and Plymouth.  Click here to learn more about the South Shore