Summary[]
Mildred Mayor has the biggest building in town, The Mayor Tower, and uses the penthouse as her office. This office has housed many a character, but most often, Mildred, who's always filling out forms and doing paperwork at her desk. Antoinette and Jane have had control over this tower, and Mildred, ever since the season three premiere.
In season five, a large alchemic blast destroys most of the tower, including the office, but Mildred (being the smart woman that she is) likely has kept all of her files safe.