From Ancestry.com Wiki
Somerset is a town in Massachusetts. It was formed in 1790 and was previously called Swansea. 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 140 Wood St., Somerset 02726. On the attached map, Somerset is shown as 13 in Bristol county.
For information about the state of Massachusetts see Massachusetts Family History Research.