Walkthrough for the Abernathy Farm area in Fallout 4.
Abernathy Farm is located south and slightly east of Sanctuary, south and slightly west from the Red Rocket Truck Stop. It should be very hard to miss, considering you can see the icon for it from the aforementioned Red Rocket Truck Stop.
Abernathy Farm is home to the Abernathy family, including Blake, Connie and Lucy. Lucy will pay you for any Melons you harvest (a patch of them can be found west of the farmhouse), but the Caps are fairly trivial (three per Melon if you don’t pass a persuasion check, five if you do). Connie will barter with you, although her wares are fairly unimpressive save for several meager shipments of various crafting supplies (cloth, concrete, fertilizer, leather and wood).
Blake Abernathy, on the other hand, will ask you to recover a locket stolen by some Raiders if you pester him enough. This starts the quest Returning the Favor, and Blake will tell you to seek out these murdering thieves at USAF Satellite Station Olivia, a short distance to the northeast.
Until you complete this quest, Abernathy Farms is of limited interest. Pretty much everything in the farmhouse is owned and will be considered stealing if you take it, although you can freely harvest any crops that happen to be growing outside. Once you complete Returning the Favor by recovering the Locket for Blake, you’ll have earned the Abernathy’s trust, and Abernathy Farm will become a new settlement for you to control.
Abernathy Farm as a Settlement
As a settlement, Abernathy Farm has a good bit going for it. It’s got a huge, rectangular build area, most of which is dirt you can build or plants crops on. The preexisting farmhouse, built into the foundation of the large electrical tower, can largely not be altered, nor can the electrical tower itself. You can remove some of the household goods within the house and build within it, but it’s largely too cluttered for any signficant development. There are also two established fields of crops - a Tato field in front of the farmhouse and a Melon patch behind it, as well as a Brahmin pen adjacent to the Tato plot. You can edit these freely if, perchance, you’d rather build on the flat ground there.
While there are some set structures you can’t change, the sheer size of the settlement’s build area makes it a non-issue. Unfortunately past the Tato plot the land slopes down, forcing you to lay down foundations if you want to build large, level structures in that direction. Ultimately this is a minor issue that just requires a bit of pre-planning and some concrete, which you might not normally need - Abernathy Farm remains an excellent settlement to develop and a prime candidate for a large, all-in-one structure almost anywhere you care to build it. The only significant downside (aside from the pre-planted Tato crops being buggy) is that there is no standing water, so you won’t be able to use Water Purifiers.