There are at least two Jersey Devils: the variety found in folklore dating at least over the range of years 1735 to 1909, and the Jersey Devil of modern sightings. The Jersey Devil of folklore is a creature that may or may not be vaguely human-shaped. It has hooves, a snake's tail, bat-wings and a head that looks something like a horse. Altogether, except for being hairy in some reports, it roughly resembles a dragon.

In fact, it was described as a dragon by many of the early witnesses. 

This Jersey devil often glows, and it can breathe fire or poison the water with its breath, both classic dragon characteristics.

 

The Jersey Devil of folklore is also known as the Leeds Devil. Local residents trace its origin to a woman named Leeds, a mistress of a British soldier who was suspected of being a witch. When she gave birth to her thirteenth child, she cursed it. The babe was born a demon-dragon and soon took to terrorizing the populace and eating children.

The Jersey Devil of modern sightings is a bunch of different things. The name has been applied to cryptids that more or less resemble the original Jersey Devil, but it is also applied to nearly every New Jersey cryptid imaginable, such as hairy humanoids that resemble Bigfoot, mystery birds, and even Eastern cougars. One "Jersey Devil" sighting described a hairy humanoid with a deer's head and glowing red eyes. A number of well-publicized but not very convincing hoaxes have managed to confuse the matter even more, scaring researchers away from whatever real Jersey Devil might or might not exist 

 

Here are some links to books you might like to read.

 

http://www.amazon.com/The-Jersey-Devil-James-McCloy/dp/0912608110 

 

http://www.goodreads.com/book/show/16138644-call-of-the-jersey-devil