The fourth floor of NYPD's 99th Precinct is the main setting for the show.
During the Pilot, much of the set is slightly different, as the show wasn't guaranteed to be picked up yet.
Bullpen
The bullpen is the open office area where the detectives of the Nine-Nine work. There are 10 desks located in the bullpen.
Scully and Hitchcock have adjacent desks, as do Jake and Amy. Terry and Gina each have their own desks.
Rosa and Charles each have empty desks attached to their own. These desks have the nameplates Sidney Brown and Casey Cook on them, though neither of these characters have been introduced.
The gate to the bullpen used to open outwards, but was switched a month before The Night Shift and now opens inwards.
Captain's Office
Captain Holt's office is adjacent to the bullpen. It has a few personal touches including a rainbow pride flag, folders arranged in a rainbow pattern and a picture of his dog Cheddar.
Briefing Room
The briefing room is where the detectives meet to be briefed on current cases. It is adjacent to the bullpen and appears to have a second entrance on the opposite side. The layout of the briefing room is often changed, the room having no definite front or back.
Holding Cell
The holding cell is located near Terry's desk. It contains several bolted-down benches and barred windows. This is where perps are kept once they are arrested.
Break Room
The break room is where the detectives hang out on their down time. It is located directly behind Terry's desk. There are a few vending machines, a sink, a game table, a couch and a boxing dummy.
Kitchen
The kitchen is located near Hitchcock and Scully's desks. It houses a table and the refrigerator, though the detectives are more often seen eating in the break room.
Evidence Room
This room is where evidence is stored.
In The Slump, Terry uses the evidence room as a location to assemble a dollhouse for his twin daughters.
During Thanksgiving, Jake notes that people do the strangest things in the evidence room when they think no one is looking. Later in Johnny and Dora, he and Amy share a kiss in the evidence room.
Interrogation Room
The interrogation room is located on the other side of the kitchen, opposite the bullpen. It contains two small rooms with a two-way mirror in between. During a flashback M.E. Time, Jake breaks the mirror by pounding on it.
Line-up Room
The line-up room also consists of two small rooms divided by a two-way mirror. It is possible that the interrogation room and line-up room are the same location.
Records Room
In the Pilot, Holt banishes Jake to the Records Room for not keeping him informed about a case. Jake remarks that the room is irrelevant (because computers exist) and covered in spiderwebs. It is likely that the room is located somewhat near the bullpen, as Holt is able to easily call in the other detectives to embarrass Jake. The Records Room has not appeared in any episodes other than the pilot.
Copy Room
The copy room is adjacent to Captain Holt's office and across the hall from the briefing room.
Balcony
The fourth floor balcony is adjacent to the bullpen. It has windows connecting to the bullpen, break room and Captain Holt's office. Charles is able to access Captain Holt's office through the balcony window during Halloween.
In Lockdown, Hitchcock gets trapped on the balcony when a white powder substance forces the fourth floor to be quarantined.
Waiting Area/Elevators/Stairs
The waiting area is the main entrance to the fourth floor. It houses a staircase and an elevator along with couches for visitors.
There is a board hanging on the wall that lists the floors of the 99th Precinct. First floor: Vice/Homicide, second floor: DEA, third floor: robbery, and fourth floor: crimes/special victims. The number next to the elevator door lets us know the detectives are on the 4th floor, however, there appears to be another floor above them as the staircase leads ups.
Restrooms
The fourth floor restrooms are noted as being down a hallway past Rosa's desk. The men's room has been seen in several episodes.
In The Slump, the men's room seems to be in bad shape, as there are no paper towels and a pipe bursts when Jake tries to flush a urinal. During Tactical Village, Holt hides out in the bathroom to secretly play Kwazy Kupcakes.
