I read that Dorsey basically divides his day into Twitter in the morning and Square in the evening, or something to that effect. I believe he lives walking distance to both offices in the Mission.
For accuracy's sake, he must live in the Tenderloin then, maybe at the NEMA apts. Twitter and Square are both in the Tenderloin, the Mission isn't really walking distance to that area (right on Market).
edit: Alternatively, he could live in the mission and then walk between the 2 offices during the day, they're right next to each other.
edit: Alternatively, he could live in the mission and then walk between the 2 offices during the day, they're right next to each other.