According to "The History of East Greenwich, Rhode Island, 1677-1960, With Related Genealogy" by Martha R. McPartland, Giles Pierce was born in 1651, probably in Portsmouth . . . he was made a freeman of Portsmouth in 1673 and in 1677 was granted land in East Greenwich . . . He served as Deputy, Moderator, and member of the Town Council. The first town meeting was held in his home in 1677.
The surname was spelled variously as Peirce, Pierce, or Pearce.
The Peirce Project web site has his year of birth as 1649.