Full disclosure: I grew up in Haverhill, so sometimes I like to write about the folklore of my home town. Here's an interesting little story from George W. Chase's 1861 book The History of Haverhill, Massachusetts.
Back in the summer of 1826, a local Haverhill man named Andrew Frink came down with a fever. Since this was long before the invention of aspirin, his fever grew and Frink became delirious. Eventually, in a fit of madness he ran from his house and disappeared.
Shortly after this, the citizens of Haverhill saw a "wild man" lurking in the nearby woods. (Unfortunately, Chase's book doesn't describe what he looked like.) Thinking he might be Andrew Frink, they formed a search party and set out to find him.
When they caught him, they were surprised to see that it was not Frink, but "literally a wild man from the woods."
"It was supposed from his appearance he was some unfortunate, who, having perhaps met with some disappointment in life, had, in a fit of insanity fled from society."
Chase doesn't say what happened to the wild man, but it seems like was he set free to roam off into the woods again. As for Andrew Frink, his body was found floating in a brook six weeks later, the victim of accidental drowning.
The idea of the wild man living on the fringes of society goes way back to ancient Mesopotamia. Wikipedia notes that medieval Celtic literature features wild men who become that way through insanity, much like the one found in Haverhill. I've seen a few other stories about New England wild men. Some are clearly human, like the famous Leather Man, while others are more cryptic and semi-mythical, like Bigfoot.
It's also interesting that without fever reducers, people would just wander off into the woods and die. If you don't have aspirin, bar the door!