It is located within the Southfield Flats, north of the larger lake adjacent to Mattock Pond and Hill Haven Ranch.
During the player's initial visit to the farm, there are two corpses, a man and a woman, inside the house who appear to have met a violent end with their blood painting the walls red. To the rear of the house is a third corpse, a woman, with a machete and a revolver next to her and, when looted, a letter is found revealing the situation unfolding at the farm.
The letter reveals the cause of the violence. The corpse in the backyard holding the letter is Annette, to whom the letter is addressed to. The note is written by Claude explaining that his wife, Harriot, is giving him a second chance presumably due to his infidelity with Annette. It seems in a fit of rage, Annette killed Claude, Harriot, and then herself.
Finding this shack along with all other shacks can net you these trophies/achievements:
Complete one of the Collectible strands
Attain 100% Completion.