Some scenes which take place in the Firehouse 51 kitchen are filmed in the actual firehouse kitchen, others are filmed on a studio set. If you see a door to the left of the cooking area, that is the studio set; if you see a drinking fountain, that's the actual firehouse.
Anthony Ferraris (Tony, Squad 3) is still an active firefighter. He helps plan how each incident occurs in the show for accuracy.
Filmed in Chicago. Firehouse 51 is actually Station 18, which is located at 1360 S. Blue Island Ave in Chicago. "Molly's Bar," owned by characters Herrmann, Dawson, and Otis, is filmed in the real Chicago bar "Lottie's" in Bucktown.
Scenes at the fire academy are filmed at the actual Chicago Fire Department's Quinn Fire Academy, located at 558 W. De Koven Street, Chicago. The academy is built on the former site of the O'Leary Farm, which is believed to be the origin of the Great Chicago Fire in 1871.
Steven R. McQueen plays a firefighter candidate named Jimmy Borelli. Steve McQueen, his grandfather, starred as a fire chief in The Towering Inferno (1974) and actually assisted real firefighters on the set when a fire broke out during filming.