The show is filmed in Chicago. The actors/actresses trained for 3 months beforehand with retired S.W.A.T. personnel and real Chicago Police officers.

Shares a universe with other shows created by Dick Wolf: Law & Order: Special Victims Unit (1999), Chicago Fire (2012), Chicago Med (2015) and Chicago Justice (2017). This means that sometimes characters of Chicago P.D. appear on his other shows and its story continues there or vice versa.

Each episode title throughout the series is taken from a line of dialog spoken in the respective episode.

LaRoyce Hawkins and Amy Morton are the only actors on the series to have actually been born and raised in the Chicago area.

A 1505 fund is an account devoted to money police had seized from people during drug-related investigation, money the department ultimately kept via the practice of civil forfeiture.

Melissa Sagemiller, Scott Eastwood, Kelly Blatz and Tania Raymonde appeared in the backdoor pilot (Chicago Fire: Let Her Go (2013)) and were all cast to be series regulars for the show's first season but were all cut before the first episode was taped. Only Sagemiller appeared in the final version of Chicago P.D.: Stepping Stone (2014).

In Chicago P.D.: The Three Gs (2015) they bust a gang leader played by Brian Tee who eventually became Dr. Ethan Choi on Chicago Med (2015).

The exterior of the station house is the Old Maxwell Street Police Station (943 West Maxwell Street) and is the same location that was used on the series Hill Street Blues (1981). It is located about half a mile from the firehouse location of Chicago Fire at 1360 South Blue Island Avenue.

The IRT or Investigative Response Team is a unit within the Detective's Bureau of the Chicago Police Department, that is responsible for investigating Officer-Involved Shootings.

Jason Beghe and Elias Koteas who play partners and friends Hank Voight and Alvin Olinsky, were born 364 days apart. Jason Beghe was born March 12, 1960, and Elias Koteas was born March 11, 1961.

COH is short for Confidential Overhear.

COPA or the the Civilian Office for Police Accountability provides Civilian Oversight (as oppose to police personnel) over the Chicago Police Department.

Voight's badge number is 32419. Lindsay's badge number is 61317. Halstead's badge number is 51163. Antonio Dawson's badge number is 50259. Kim Burgess's badge number is 59686. Alvin Olinsky's badge number is 50037.

Ventra is an electronic fare payment system for Public Transit within the Chicago Metropolitan Area.

NVLS is short for National Vehicle Location Service, which is located in Livermore, California and is a subsidiary of Vigilant Solutions. It is essentially a database of automobile license plates and the corresponding locations and time-stamps of where the vehicles were found.

Hank Voight's caller ID is 5020. Erin Lindsay's caller ID is 5021 Lincoln. Jay Halstead's caller ID is 5021 George. Antonio Dawson's caller ID is 5021 Frank. Adam Ruzek's caller ID is 5021 Ida. Hailey Upton's caller ID is 5021 Henry. Kim Burgess' caller ID is 5021 Eddie. Kevin Atwater's caller ID is 5021 David.

In the squad room, as shown on the Investigative Board, there is cryptic alphanumeric string next to the suspect's photo, as seen in the example, M/1/19. The first part of the string refers to the Gender of the suspect (Male/Female, or M/F) and the third part is the suspect's age. With respect to the second part, according to a Chicago Police Directives, racial identification parameter is assigned a code number. 1 - BLACK 2 - WHITE 3 - BLACK-HISPANIC 4 - WHITE-HISPANIC 5 - AMERICAN INDIAN/ALASKA NATIVE 6 - ASIAN/PACIFIC ISLANDER

In series such as In the Heat of the Night (1988), the violent crime is exaggerated, such as one or more murders each week. The opposite is true here- there is far more crime in Chicago than what is depicted. Season 1 premiered on January 8, 2014 and ended on May 21, 2014. According to the Chicago Tribune, during the months of January through May 2014, there were 141 criminal homicides in Chicago. In all of 2014, there were 415. Season 2 premiered on September 24, 2014 and ended on May 20, 2015. According to the Chicago Tribune, during the months of January through May 2015, there were 164 criminal homicides in Chicago. In all of 2015, there were 473. Season 3 premiered on September 30, 2015 and ended on May 25, 2016. According to the Time magazine, in all of 2016, there were 762 criminal homicides. Season 4 premiered on September 21, 2016 and ended on May 17, 2017. According to the Chicago Sun-Times, in all of 2017, there were 664 criminal homicides. The Chicago Tribune reported that as of October 9, 2017, 2,958 people had been shot in Chicago. Season 5 premiered on September 27, 2017 and ended on May 19, 2018. According to the Chicago Sun-Times, in 2018 through December 25, there were 555 criminal homicides. The Chicago Tribune reported that as of July 9, 2018, 1,433 people had been shot in Chicago.

In 1974, Office of Professional Standards (OPS) was created to provide Civilian Oversight into the Chicago Police. In 2007, it was superseded by Independent Police Review Authority (IPRA). In 2016, City Council voted to replace it by Civilian Office of Police Accountability, which was implemented in September 2017. The difference being, a bigger budget and expanded jurisdiction (domestic violence, excessive force, coercion, and verbal abuse," and, "cases in which a department member discharges his or her firearm, stun gun, or taser in a manner which potentially could strike an individual," as well as investigations into the death of individuals in police custody).

A&A is short for Attendance and Assignment Record used to keep track of Chicago Police Department personnel.

John Pankow guest stars as a judge friend of Voight's(Jason Beghe) on a couple of episodes. The two of them starred together in Monkey Shines(1988).

St. Francis. is the Patron saint of gratitude.

POD is short for Police Observation Devices, otherwise known as Surveillance or Lamp Post Cameras.

DTO is short for Drug Trafficking Organization.

An I.R. Number is a Individual Record Number assigned by the Chicago Police to an individual upon his or her arrest. This number is used in any subsequent arrests of the same individual. It may be possible for two names to be listed for the same I.R. number if both names refer to the same person.

Street and Sans refers to the Department of Street and Sanitation.

CSLPO is an FBI acronym which stands for Corruption of State and Local Public Officials.

In the United States, an "open carrier" ( also known as a "open microphone", "keyed microphone", or "open radio") is police parlance for a radio that has been inadvertently left on in Talk/Transmit mode. An open carrier stalls and paralyses broadcast traffic, leaving so-called "dead air" to reveal sudden gaps, smudges of hiss, gently swaying drones, beeping alerts, fragmented words, quick phrases, recessed conversations, and other unexpected artifacts. It's like butt-dialing everyone who is listening to the radio.

CHRIS is short for Criminal History Records Information System

OEMC is short for Office of Emergency Management and Communications.

"MUD'S and Toll's " - MUD is short for "Message Usage Details" and refers to local calls, and Toll refers to an itemized listing of Long Distance calls.

ERPS is short for Evidence and Recovered Property Section.

"Over the zone" refers to a radio message received over the "zone frequency". In Chicago, the "zone",is another word for police district.

Jay Halstead is said to have grown up in the Canaryville neighborhood of Chicago. The western border of that neighborhood is a street named S. Halsted St.

Actor Kevin J. O'Connor made several guest appearances on season two and two episodes of season three as Commander Fischer

On Season 4 Episode 8, when Voight and then the victims wife touch the memorial wall you can see Joseph Sikora's name. Which is the name of the actor's who portrayed Justin's killer in the previous season.