J'town, the core setting of Dark Places & Demogorgons has it's own setting guide. The book clocks in at 140 pages. As you can see from the picture to the right, the back cover has a simple map of the area.
The guide starts with an overview and timeline for J'town. There's a nice section on colloquial phrases. This was a cool addition, though I didn't really need it. I'm originally from Appalachian southern Ohio and grew up on the Ohio River. That would put J'town a few hours from where I grew up. I've heard many of the phrases mentioned growing up (and may still use some depending on the company I'm with).
After this preliminary info five districts/broad areas of J'town are described. Each section includes places of note, with descriptions of relevant npc's and adventure/story hooks. These are incredibly useful when running a game. One of my favorite locations mentioned through these sections is The Cat's Meow. It's a dive bar owned by a man with my last name (Isaac). I really dig this because my family is from coal mining country in Kentucky.
Two important locations are given more description. The first is the local magic shop and the second is the high school. Let's be honest, since the characters are teens, this high school section is extremely valuable. Teachers and cliques are given attention. There's even a "determine your classes table" which is super helpful. The magic shop includes an important npc and several magical items, which is pretty cool. This is followed by descriptions (and some stats) of important citizens and groups.
The book ends with adventure seeds (presented in the monster of the week style format of the core) and monsters. This section is a nice compliment to those in the core. My favorite adventure seeds are the ghost pug and the new girl. A really important antagonist mentioned in the corebook is given much more detail in this section, the head of J'town's satanic panic, Reverend Phillips, is discussed and statted out. His stats include some really interesting holy relics and mythos items. He also has an elite group of followers called the Council of 13 and their stats are given as well.
If your DP&D game is going to be set in J'town, you'd be a fool to pass this one up. Even if it's not I think there's enough good material to warrant this one if you run the game.
All DP&D books can be found on Lulu and OBS, but I recommend ordering here, directly from Bloat Games.