This is a classic book! Inspired by a unique wild horse roundup on the east coast of Virginia, Marguerite Henry spent time on Chincoteague Island, talked to locals including the Beebe family, learned about the centuries old tradition of Pony Penning, and bought a palomino pinto filly named Misty, out of a black pinto mare named Phantom, by a chestnut pinto stallion named Pied Piper. That much is real life.
The rest she fictionalized into a ripping good yarn that evokes the unique qualities of island life.
Visiting Chincoteague, and the outlying barrier island of Assateague today, you'll still find most of the flavor of the islands much like it was in the books.
I was lucky to visit the islands in 1972, the last year Misty was alive, and met her. One pony, one story, put this tiny gem of the Atlantic coast on the map forever. Misty and Stormy are partly responsible for helping rebuild the pony herd after the devastating 1962 Ash Wednesday Storm, written about in Stormy: Misty's Foal. That storm also opened the way for the Park Service to claim Assateague as parks and refuges, undeveloped, safe for wildlife and the pony herds.
If you can, see the classic 1961 film. It is from a simpler time, and was filmed largely on the islands. Misty's hoofprints are in the concrete in front of the Island Theater.