The Jersey Devil is a folkloric monster as well as a cryptid that is either seen to be supernatural entity akin to a demon or an unidentified animal or creature that stalks a region of New Jersey known as the Pine Barrens.
According to local folklore, the origin of the creature came from the Leeds family, a local clan of layabouts and misfits headed by a drunken patriarch and constantly pregnant mother. On learning that she was pregnant a thirteenth time, she prayed, "Lord, let this one be a devil".
Nine months later, Mother Leeds reportedly gave birth to a healthy, blond haired, blue-eyed boy. Unfortunately, her prayers were answered. The boy's eyes turned burning red, as his hair suddenly grew coarse and black as coal. His skin became leathery, as two wings sprouted from his back. His nose turned into a snout, his feet morphing into cloven hooves. Legends differ, arguing that the baby killed his mother, killed everyone present, or just flew away in the chimney.
For centuries since, people have claimed that something stalked the Pine Barrens, a strange animal that looked like nothing they had ever seen before. The creature was blamed for livestock killings in the region, and even Napoleon's brother Joseph reportedly fired on the creature during a hunting trip in Bordentown. These sightings were typically localized, however, and the creature faded into folklore.
From January 16th to the 23rd, dozens of sightings were reported through the Deleware Valley region between Pennsylvania, Deleware, and New Jersey. The Devil reportedly killed livestock, attacked a trolley car in Haddon Heights, NJ, and a social club in Camden, NJ. Police in Bristol, PA, reportedly fired on it to no effect, and members of the Philadelphia Fire Department stated they managed to fight the creature away with hoses. The panic forced businesses and schools to close, as the Philadelphia Zoo offered a still-present $10,000 reward for the creature. So far, the reward remains unclaimed.
For years, many have claimed the Devil is simply a misidentified heron, a local bird to the region with a massive wingspan and distinctive long beak. The misidentification is typically attributed to another explanation, the fact that the residents of the Pine Barrens have a reputation.
The Pine Barrens are highly acidic, meaning that farming is almost impossible in the sandy soil covered in pine trees. The residents, called "Pineys", are often considered along the same vein as the hillbillies of Appalachia, shiftless and untrustworthy. Anyone living there at the time the legend is said to have began were often the outcasts and dregs of colonial society. This unsavory reputation could have easily given birth to tales warning travelers away from the region.
The Jersey Devil is a highly regional cryptid, despite various nationwide portrayals. The most prominent is the New Jersey Devils hockey team, which travels the US and Canada, and spreads the legend simply by word of mouth of sports fans.
The X-Files episode "Jersey Devil" claims to focus on the creature, but instead appears to focus on a Bigfoot/feral human monster of the week, completely ignoring the actual legend of the Devil. Presumably this can be attributed to the fact that the special effects needed to actually recreate the more common legend of the creature wouldn't be available to the show for many years to come.