Its exterior is of a large gray church. After its abandonment during the early 21st century, the Institute is in a state of disrepair, with broken black windows and a missing front door. The Institute also had a garden, now a mess with no one to maintain it. In the garden are several statues, now covered with moss, including a rearing horse, a stone woman holding a dainty parasol, tiny stone rabbits, and a boy with a bird perched on his wrist—the last of which was used as a hiding place for messages.
The Institute was once famous for having a considerably large selection of books on dark magic, including the original Malleus Maleficarum, the Daemonatia, and previously, the Black Volume of the Dead.
The Cornwall Institute is the first Institute on the British Isles.
In the early 1800s, the Institute was run by Felix Blackthorn and housed his family. During this time, the Blackthorns took in a young warlock named Malcolm Fade, who eventually fell in love with Felix's daughter Annabel. Due to the attitude towards Shadowhunter-Downworlder relationships at the time, the lovers decided to run away. The couple tried steal the Black Volume of the Dead but got caught, and the book was returned to the Institute.
Some time after the Dark War in December 2007, the Institute became abandoned due to the shortage of Shadowhunters after the war, leaving the Institute with no one to manage it. In 2012, Kit Herondale and Tiberius Blackthorn Portaled to the Institute to leave a message for the resurrected Annabel.
- Annabel Blackthorn
- Felix Blackthorn † (former head; 1800s)
- Felix's nephew †
- Malcolm Fade † (former ward)
- Blackthorn family