Many New England ferns are common in much of the world, while quite a few grow around here and nowhere else. The term "endemic" can simply mean very abundant, but it is used botanically to designate plants which grow only in one region.
For example, consider Thelypteris simulata.
The common name is Massachusetts Fern. The type population is probably from Ponkapoag Pond in the Blue Hills. It was named in 1894, having been overlooked for years for being similar to the other two local Thelypteris.
Of those New England Ferns which are globally widespread, most are circumboreal; we share most of our pteridophytes with Canada and Michigan (or Wisconsin), and many with north Asia.
A counterexample is the genus Pellaea, or Cliff-brakes. They migrated here from southwestern U.S., and look as though they should be in a desert somewhere.
Visit the Flora of North America website for range maps of all the ferns.