In South Jersey and Philadelphia folklore in the United States, the Jersey Devil, also known as the Leeds Devil, is a legendary creature, or cryptid, said to inhabit the forests of the Pine Barrens in South Jersey. The creature is often described as a flying biped with hooves, but there are many variations. The common description is that of a bipedal kangaroo-like or wyvern-like creature with a horse- or goat-like head, leathery bat-like wings, horns, small arms with clawed hands, legs with cloven hooves, and a forked or barbed tail. It is also said that it has a strange elongated body and a thick tail. It has been reported to move quickly and is often described as emitting a high-pitched "blood-curdling scream".

The popular legend of the Jersey Devil or Leeds Devil is dated variously, and is almost invariably attached to the "The Pines", or the South Jersey Pine Barrens, and sometimes specifically Leeds Point within the Pine Barrens. The devil's mother is usually a woman named Leeds, or "Mother Leeds" of Burlington, but other names such as the Shourds have occasionally been forwarded.

According to one précis, in 1735, a woman named Leeds had twelve children and, after discovering she was pregnant for the thirteenth time, cursed the child in frustration, declaring, "Let the child be the devil!". The child, though born normally, immediately grew wings, a tail, and claws after birth and flew out to the Pine Barrens.

According to some, the child transformed into a creature with hooves, a goat's head, bat wings, and a forked tail. Growling and screaming, the child beat everyone with its tail before flying up the chimney and heading into the pines. In some versions of the tale, Mother Leeds was supposedly a witch and the child's father was the devil himself. Some versions of the legend also state that local clergymen subsequently attempted to exorcise the creature from the Pine Barrens.

In a different telling, localized not at Leeds Point but at Esteville, near Mays Landing, a Mrs. Leeds became pregnant around 1855 and rejected her baby, wishing a stork would deliver a devil. Thus a winged devil was born and flew out the window; it would intermittently return but the mother would shoo it away.

Prior to the early 1900s, the Jersey Devil was referred to as the Leeds Devil or the Devil of Leeds, either in connection with the local Leeds family or the eponymous Leeds Point in South Jersey.

"Mother Leeds" has been identified by some as the real-life Deborah Leeds, on grounds that Deborah Leeds's husband, Japhet Leeds, named twelve children in the will he wrote during 1736, which is compatible with the legend. Deborah and Japhet Leeds also lived in the Leeds Point section of what is now Atlantic County, New Jersey, which is commonly the location of the Jersey Devil story.

Brian Regal, a historian of science at Kean University, theorizes that the story of Mother Leeds, rather than being based on a single historical person alone, originated from the reputation of the local prominent Leeds family in the southern portion of the colonial-era Province of New Jersey, where religious-political disputes became the subject of folklore and gossip among the local population. Regal contends that folk legends concerning these historical disputes evolved through the years and ultimately resulted in the modern popular legend of the Jersey Devil during the early 20th century. Regal contends that "colonial-era political intrigue" involving early New Jersey politicians, Benjamin Franklin, and Franklin's rival almanac publisher Daniel Leeds (1651–1720) resulted in the Leeds family being described as "monsters", and it was Daniel Leeds's negative description as the "Leeds Devil", rather than any actual creature, that created the later legend of the Jersey Devil.