Truck Company 81 (commonly called Truck 81) is the secondary apparatus assigned to Firehouse 51. The original rig was a 1996 Seagrave Marauder equipped with a 100' rear-mount ladder, space for other equipment and seating for up to eight firefighters. The truck is staffed by 4-5 firefighters.
In the Season 3 episode "Just Drive the Truck", the truck is written off in a collision with Truck 66 and the firehouse is given a "new" rig as a replacement. (They actually receive an older version of the CFD's ladder truck.)
In S08E13, Truck 81 receives a "new" apparatus - a 1990 Spartan Gladiator (formerly of the La Grange Park Fire Department and repainted into the traditional CFD paint scheme for the show.) This "new" rig is configured as a 'quint' (pumper/aerial combination) and is equipped with a 1250 gallon-per-minute (GPM) pump, 200-gallon water tank and a 110' aerial ladder.
- Company Officer - Captain Matthew Casey
- Engineer/Driver - Lieutenant Stella Kidd
- Firefighter - Randy McHolland
- Firefighter - Blake Gallo
- Andrew Darden - Deceased, killed in the line of duty.
- Jose Vargas - Transferred to Squad 3, later placed on long term disability.
- Peter Mills - Transferred to Squad 3, currently resigned from the CFD.
- Rebecca Jones - Deceased, committed suicide.
- Joe Cruz- Transferred to Squad 3.
- Jimmy Borrelli - Transferred to Ambulance 61 due to manpower, then returned. Later placed on long term disability.
- Gabriela Dawson - Transferred back to Ambulance 61 due to manpower. Resigned from CFD to join humanitarian relief efforts in Puerto Rico.
- Jake Cordova - Temporary replacement for Brian Zvonecek after he was shot.
- Christopher Herrmann - Promoted to Lieutenant and assigned to Engine 51.
- Brian Zvonecek - Deceased, killed in the line of duty.
- Darren Ritter - Temporary replacement for Brian Zvonecek after his death.