CitiHall is a municipal building in New New York. It houses the office of the Mayor, currently C. Randall Poopenmeyer. Also, Mrs. Astor and her butler, Hobsy, are known to have been in it. The building is probably located in Manhattan.
A community recycling event was held at the building. It was also where Leela got passes for her parents to come up from the surface.
It's name is a tongue-in-cheek reference to the multinational bank, Citibank. It is also the 31st century equivalent of the New York City Hall from the 21st century.