In the early 1800s the Cornwall Institute was run by Felix Blackthorn and his family. Around this time the Blackthorns took in a young warlock named Malcolm Fade. Malcolm eventually fell in love with Felix's daughter Annabel, and due to the attitude towards Shadowhunter-Downworlder relationships at the time, the lovers decided to run away. Malcolm then stole the Black Volume of the Dead from the Institute, where it was being kept.
In 2007, during the Dark War, the residents of the Cornwall Institute were killed and, since there were no longer enough Shadowhunters to man it, the Institute was abandoned.
The Cornwall Institute is a large grey church surrounded by sloping lawns. It is very close to the sea, which can be seen in the distance. After being abandoned for so long the Institute is in a state of disrepair, and resembles a heap of gray stone with broken black windows and a missing front door.
The Institute's garden is also very messy, full of overgrown grass and weeds. The garden is scattered with old, moss-covered statues that include a rearing horse, a boy with a bird perched on his wrist, a stone woman holding a dainty parasol, and tiny stone rabbits.
- Felix Blackthorn † (former head)
- Annabel Blackthorn
- Felix's nephew †
- Malcolm Fade (former ward)
- Blackthorn family
- A Portal, built in 1903, exists in the London Institute which leads directly to the Cornwall Institute.
- The statue of the boy with the bird was used as a hiding place for messages between Malcolm and Annabel.