Horror is very popular now which makes some library workers uncomfortable because it is a genre they personally avoid. There are plenty of resources out there to help you do don't be scared!
Remember that I am trying to avoid repeating resources in these guides. You will find horror information on some of the science fiction, fantasy, and crime fiction guides.
One site you should have bookmarked is Becky Spratford's blog for horror fiction, RA for All - Horror. She posts reviews, trends, and other vital information about horror fiction. There is plenty of detail about the major horror awards such as the Stoker Awards and the Splatterpunk Awards. In addition, it is the place to find information about Summer Scares. A project to promote reading horror in the summer, Summer Scares is a joint effort of United for Libraries, Book Riot, Booklist, The Horror Writers of America, and NoveList, a division of EBSCO Information Services. Three titles are picked for adults, young adults, and middle grade readers. An author is selected to be the spokesperson for the year as well. It's a great way to add horror to your summer displays. The Springfield-Greene County (MO) Library creates a programming guide each year for use by libraries at no charge. A link to that is also on Becky's Summer Scares resource page. Horror themed programming is a nice way to change up your usual summer programming fare.
ReadJumpScares by Emily Hughes includes information about horror novels including her very valuable list of this years' upcoming horror novels. Her website also lists what she has written about horror on a variety of websites.
The Horror Writers Association is the premier organization for those interested in horror and dark fantasy. The organization issues the annual Bram Stoker Awards. In addition to a blog with interviews and information about a variety of people from the world of horror, they also have a strong interest in helping libraries promote horror. You can reach out to them for information including how to find an author to speak at your library.
Founded by authors Brian Keene and Wrath James White, the Splatterpunk Awards are presented annually at KillerCon. These awards are focused on splatterpunk and extreme horror. These subgenres of horror have been growing in popularity and I have found that the winners of these awards circulate well.
Cemetery Dance was founded by author Richard Chizmar in 1988. Besides publishing books, they also feature news and reviews on their website. The right hand sidebar has links to series like "Brian Keene's History of Horror Fiction."
Horror DNA is a site with news and reviews from all over horror including books, TV, movies, and video games.
A long time standard bearer of horror, Fangoria magazine also features news and review from horror TV, movies, books, and more. They also have four podcasts.
If you have more resources, add them below. Also, don't forget to check out my other genre guides for sites with horror information.