Martha's Vineyard Island
Martha's Vineyard, an island five miles off the southeastern shore of Massachusetts in the U.S., is notable for its history of the majority of sign language users. The population on the Martha's Vineyard island in the 18th century had a high rate of deaf heredity. Almost all inhabitants, both deaf and hearing, knew an indigenous signed language, called Martha's Vineyard Sign Language (MVSL).
Most of the deaf inhabitants on the island may be traced their ancestry back to a small region in southern England, known as the Weald in the county of Kent. Some Kentish Weald families emigrated from there to Massachusetts. The first deaf settler and his hearing wife moved to the island in the late 17th century. An incidence of genetic deafness had spread. So was the language, probably originally from England. Eventually, nearly every inhabitant, both deaf and hearing, used MVSL. As nearly everyone was bilingual, deafness was not a concern. Sometimes, hearing inhabitants talked to each other in sign language even without deaf people present.
As the first school for the deaf was founded in Hartford, Connecticut, many deaf students from the island attended this school. Their language was intermingled with Old French Sign Language, which was brought by the French deaf teacher, Laurent Clerc, from France. Eventually, these island inhabitants settled down on the mainland. A number of signers on the island eventually declined till the mid-20th century. In the meanwhile, tourism and its economy grew on the island. The last deaf person born on the island died in the 1950s.
Groce, Nora Ellen. Everyone here spoke sign language: Hereditary deafness on Martha's Vineyard. Harvard University Press. 1985.