Hollows - Series by Kim Harrison

A few decades back, a genetically engineered virus wiped out  a big chunk of normal humans, leaving the supernatural Inderlanders - including witches, vampires, werewolves, and others - to help put civilization back together. 

Rachel Morgan is a witch and bounty hunter in this strange alternate world - and a very popular person, if you judge by the number of people out to kill her. 

Tags: demons, urban fantasy, vampires, werewolves, witches