Chicago P.D. season 4

The fourth season of Chicago P.D., an American police drama television series with executive producer Dick Wolf, and producers Derek Haas, Michael Brandt, and Matt Olmstead, premiered on September 21, 2016 and concluded on May 17, 2017. The season contained 23 episodes.

Regular

 * Jason Beghe as Sergeant Henry "Hank" Voight
 * Jon Seda as Senior Detective Antonio Dawson (episode 1–8)
 * Sophia Bush as Detective Erin Lindsay
 * Jesse Lee Soffer as Detective Jay Halstead
 * Patrick John Flueger as Officer Adam Ruzek
 * Marina Squerciati as Officer Kim Burgess (episode 1-19 and episode 20-23 credit only)
 * LaRoyce Hawkins as Detective Kevin Atwater
 * Amy Morton as Desk Sergeant Trudy Platt
 * Elias Koteas as Undercover Senior Detective Alvin Olinsky

Recurring

 * Samuel Hunt as Greg "Mouse" Gerwitz
 * Barbara Eve Harris as Commander Emma Crowley
 * Markie Post as Barbara "Bunny" Fletcher
 * Chris Agos as Assistant State's Attorney Steve Kot
 * Esai Morales as Chief Lugo
 * Nick Wechsler as Detective Kenny Rixton
 * Li Jun Li as Officer Julie Tay
 * Jules Willcox as Nicole Silver
 * Kevin Kane as Officer Mike Sorensen
 * Ian Bedford as Commander Ed Fogel
 * Tony Crane as Jimmy Sanguinetti
 * Tracy Spiridakos as Detective Hailey Upton

Special guest star

 * Billy Burke as Jake McCoy
 * Arthur-Angelo Sarinas as Loo

Crossover

 * Jesse Spencer as CFD Lieutenant Matthew Casey
 * Taylor Kinney as CFD Lieutenant Kelly Severide
 * Monica Raymund as CFD Paramedic Gabriela Dawson
 * Eamonn Walker as CFD Battalion Chief Wallace Boden
 * David Eigenberg as CFD Firefighter Christopher Herrmann
 * Yuri Sardarov as CFD Firefighter Brian "Otis" Zvonecek
 * Christian Stolte as CFD Firefighter Randy "Mouch" McHolland
 * Kara Killmer as CFD Paramedic in Charge Sylvie Brett
 * Nick Gehlfuss as Dr. Will Halstead
 * Torrey DeVitto as Dr. Natalie Manning
 * Yaya DaCosta as Nurse April Sexton
 * Rachel DiPillo as Dr. Sarah Reese
 * Colin Donnell as Dr. Connor Rhodes
 * Brian Tee as Dr. Ethan Choi
 * Marlyne Barrett as Nurse Maggie Lockwood
 * S. Epatha Merkerson as Sharon Goodwin
 * Oliver Platt as Dr. Daniel Charles
 * Carl Weathers as State's Attorney Mark Jefferies
 * Philip Winchester as Assistant State's Attorney Peter Stone
 * Jon Seda as Chief Investigator Antonio Dawson
 * Monica Barbaro as Assistant State's Attorney Anna Valdez
 * Deanna Reed-Foster as Tina Cantrell
 * Nora Dunn as Dr. Richardson

Casting
Li Jun Li joins the cast as Officer Julie Tay for a three episode guest spot. She is set to replace Brian Geraghty's character Officer Sean Roman as Officer Kim Burgess' (Marina Squerciati) partner, after he left the series at the end of last season. On September 28, it was reported that Jon Seda as character Antonio Dawson would move from P.D. to Justice, where Antonio became an investigator for the SA's office. It was further reported on October 5 that Seda's last episode of P.D. would be episode 8.

Nick Wechsler joins the cast as Kenny Rixton, a former protégé of Voight's, for a multi-episode arc. On February 7, 2017, it was revealed that Esai Morales join the cast as Chief Lugo, a veteran of the Police Department who is trying to steer the CPD into a new style of policing. His first appearance was in the three-way crossover with Chicago Fire and Chicago Justice, before recurring throughout the remainder of the season.

Set to recur as Hailey Upton, a robbery homicide Detective, Tracy Spiridakos joins the cast, with her first episode slated to air in early May. Squerciati took maternity leave from the show in March 2017, and Kim made her temporary departure in "Last Minute Resistance".

Crossovers
A crossover starting on Chicago Fire and concluding on Chicago PD aired on January 3, 2017.

A three-way crossover between Chicago Fire, Chicago PD and the premiere of Chicago Justice aired on March 1, 2017, with heavy involvement from Chicago Med.