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.

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).

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

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.

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.

COH is short for Confidential Overhear.

Ruzek is left-handed. Patrick John Flueger is left-handed as well.

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

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.

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

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.

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

St. Francis. is the Patron saint of gratitude.

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

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.

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

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).

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).

OEMC is short for Office of Emergency Management and Communications.

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