From Ancestry.com Wiki
Swansea is a town in Massachusetts. It was formed in 1667 and was previously called Rehoboth. It can be found in Bristol county and is a part of the Northern registry of deed district. For more information, contact the county at 81 Main St., Swansea 02777. On the attached map, Swansea is shown as 12 in Bristol county.
For information about the state of Massachusetts see Massachusetts Family History Research.