Millennium (1996 - 1999)
This was conceived as a psychological thriller, but it could also be classified as a horror, particularly when you reach season two and a lot of the episodes seem to have demons in. I think episodes like "Wide Open" (season one) and "Saturn Dreaming of Mercury" (season three) definitely feel very horror like; the former is about a killer who comes into a home during an open house viewing, hides in the wardrobe, then comes out at night and kills the parents.
A lot of the directors seemed to take inspiration from David Lynch, another reason why this feels like a horror.
Day 22: Favorite Horror TV Series
Day 23: Favorite Horror that comes from a Book
Day 24: Best Horror Movie You Saw Last Year
Day 25: Favorite Classic Horror Movie
Day 26: Favorite Horror Movie Series
Day 27: Least Favorite Horror Movie
Day 28: Favorite Horror Movie Made for Kids
Day 29: Favorite Jump Scare
Day 30: Favorite Plot Twist
Day 31: Favorite Horror Movie