DukesCounty: formed in 1695 from Martha's Vineyard and the Elizabeth Islands, which had been part of DukesCounty, NewYork until Massachusetts gained it in 1691.
In 1679 the county was eliminated when most of the county became part of the colony of New Hampshire and the remainder was added to Essex County.
YorkCounty formed in 1652 from unorganized land in the Maine District with the name Yorkshire County.