The Twisted Ones by T. Kingfisher

The Twisted Ones is a folk horror novel by Ursula Vernon, writing as T. Kingfisher, about a young woman named Mouse who cleans out her deceased grandmother's hoarded house in rural North Carolina and discovers her step-grandfather's journal detailing terrifying, otherworldly creatures from a "Green Book". The journal entries seem like ramblings until Mouse encounters the creatures herself, leading her on a journey into a hidden, dangerous world to save her dog and confront the "holler people". It's known for its witty narration, Southern gothic atmosphere, and blend of humor with genuine scares, drawing inspiration from Arthur Machen's "The White People"