Taken from IGN

Rumors suggest that Bethesdas next Fallout game will take place in Boston. According to a thread posted by an anonymous Reddit user, scouting is currently underway at the Massachusetts Institute of Technology. The rumors are true, Fallout 4 will take place in Boston, the user writes. In case you haven't heard, Bethesda has recently been scoping out and researching Boston. They also have a strong connection to MIT. The user notes that he may or may not be an MIT employee but that's really all I can say for fear of losing my job.

The rumor makes sense considering the lore behind The Commonwealth, the Fallout universes version of Massachusetts thats been referenced in prior games. In Fallout 3 side quest The Replicated Man, players encounter a scientist named Dr. Zimmer who comes from The Commonwealth, a war-ravaged quagmire of violence and despair where he notes he and his colleagues created androids that have escaped and are running wild. Zimmer also references The Institute, which is presumably a future version of MIT.

As noted by our friends over at Gamespy, The Commonwealth also contains the Railroad, which runs in direct opposition to the Institute and aims to rescue the androids that have been created. A branch of the Commonwealth Police known as the Synth Retention Bureau is in charge of capturing androids that have escaped from the Institute.

Bethesda has declined to comment on the rumor of a Boston setting for now, but considering the impressive amount of mythology already revolving around The Commonwealth, it certainly seems like a plausible theory.

Bethesdas Fallout 3 was released in 2008 and took place in a war-ravaged version of Washington DC, with expansions adding Pittsburgh and Maryland. Follow-up Fallout: New Vegas was developed by Obsidian in 2010 and was set in a future version of Nevada.

Well the game isn't out yet and it hasn't officially been announced so we are still in the dark to be honest...