In 1814, numerous people throughout the city of London, England reported seeing a pig's head silhouetted by gaslight from within the confines of a passing carriage. At times, they even saw a piggish snout protruding from the carriage window. The legend of the Pig Lady was born, and through discussions in various newspapers, the theory was reached that it was a wealthy young woman from Manchester Square - this was none-too-complementary to the young woman in question! St. Bartholomew's Fair in London exhibited the "Pig Lady", which was actually a shaved bear in a dress.
It is tempting, however, to speculate whether the English could have imported the legends when they settled Cecil County, Maryland, because legends of the Pig Lady exist in Elkton and Rising Sun, both in that county.
The Elkton variant has it that she was a survivor of a house fire who fled into the forest, eventually taking up residence underneath Pig Lady Bridge near town. Sometimes the squeals and grunts of a pig are heard, but usually she magically makes your car stall and then she comes out and kills you with an axe. This makes her yet another of the bloodthirsty half-humans of Maryland lore, and she takes her place in the urban legend pantheon alongside Bunnyman, Boaman and Goatman.
Oh, she's also sometimes supposed to be an inbreeding Dupont, which ties the legends of the Pig Lady in with those of the Devil's Woods in Chester County, Pennsylvania. I'm not exactly sure why she's haunting a bridge in Elkton, Maryland rather than her family's estate, the Cult House, but there it is. One wonders if this helped to influence the swinish look to the monsters in M. Night Shyamalan's The Village, filmed in the Devil's Woods.
The versions in Rising Sun make her a a denizen of Lover's Lane - well, sort of, as she attacks the cars of necking teenagers in the Rising Sun town dump, surely one of the most romantic spots I can think of. This Pig Lady bangs on the side of the car until the teenagers drive away in search of a spot where they can continue their amorous encounter in peace.
Or maybe she haunts another old wooden bridge. Sometimes passersby's cars will stall and they'll hear scraping sounds. Then when they finally manage to drive away they'll find the hoofprints of the Pig Lady indented on their car.
Maybe the idea of a murderous, swine-faced humanoid sounds to you like a reject from the Saw movies or something out of an Insane Clown Posse song, but the stories have been around for generations.