The New York City Hall is the chief administrative building of the City & County of New York.
During the Plasmic Strainer incident, the Ghostbusters visited Mayor Lenny's office twice to apprise him of the situation. Like most of New York, City Hall was inundated with slime from the Slimers. For the second visit, the Ghostbusters asked Lenny for helicopters. Before Lenny could give his answer, Slimer reached into the office and kidnapped Janine Melnitz. Lenny relented and gave the Ghostbusters what they wanted.
In 1997, Piper met with Mayor McShane in his office and made a deal. McShane later refused to cater to his extra demands, reneged on the deal, and had him thrown out, not knowing Piper was a ghost. The Extreme Ghostbusters later visited City Hall and tried to warn McShane about Piper. But it was too late.