Commonwealth (5e Fallout Campaign Setting)
From D&D Wiki
The Commonwealth, also known as the Commonwealth Wasteland, is the setting of Fallout 4. It is home to what remains of Boston and the Institution (If you decide to play a campaign before the main story of Fallout 4). This region is home to a lot of American history, especially in the Revolutionary War. In this Wasteland you can find major settlements like Diamond City, Sanctuary, and the Castle. The Commonwealth also houses the Glowing Sea, which is ground zero of the nuclear strike. Now this New England region is owned by Raiders, Gunners, and a lot of Mirelurks.
This environment has a Radiation Storm that is similar to a Thunderstorm but the storm brings mass amounts of Radiation. Most people board up in the nearest shelter and wait out the storm. Aside from Storms, the environment is for the most part livable, allowing farming to occur in settlements. Most of the water has radiation but basic filtration can clear most of it up. A lot of wildlife lives in the Commonwealth so random encounters with Molerats, Mirelurks, Yao Guai is not uncommon.
The Glowing Sea offers more danger to PC as there is a large numbers of Radscorpions, Feral Ghouls, and Deathclaws. Large amounts of radiation can found here too.