Demons are supernatural creatures that plague Purgatory and the rest of the world.
- The Widows
- Bulshar Clootie
- Poppy (half demon)
- Porcelain Doll
- The Vampires Doc, Kate, Otto, and Petra
- Possession: The Mictian can inhabit human bodies and the Porcelain Doll is seen inhabiting a painting.
- Demon Eyes: Humans possessed by the Mictian will have completely black eyes when Mictian is in control.
- Super Strength: When Waverly Earp is possessed by Mictian, she is seen lifting and choking Tucker Gardner with one hand.
- Limb Regeneration: Waverly and Wynonna Earp were both able to regrow limbs while possessed by Mictian.
- Wish Fulfillment: Marzaniok is able to grant the wishes to whoever makes a deal with him.
- Venomous: The Widows are able to release a paralyzing venom via a bite and by exhalation.
- Sleep Powers: The demon Hypnos has the ability to cause the entire town of Purgatory to fall into a month long sleep.
Most demons can be killed by a shot from Peacemaker, with The Widows and Bulshar Clootie (probably) being the exceptions.