If you’ve ever tried to dive into NBC’s One Chicago universe, you know it’s no small task. Spanning four main shows — Chicago Fire, Chicago P.D., Chicago Med, and the short-lived Chicago Justice — plus a handful of Law & Order: SVU tie-ins, the franchise is massive. Watching it all in proper order ensures you don’t miss any key crossovers or emotional connections between characters.
Here’s your complete guide to watching all the One Chicago series in chronological order, including every crossover event.
1. Start with Chicago Fire (Season 1)
The One Chicago universe began with Chicago Fire in 2012. You can safely watch Season 1 straight through — it sets up the world of Firehouse 51 and introduces fan favourites like Casey, Severide, Dawson, and Chief Boden.
Important Episode:
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Chicago Fire Season 1, Episode 23 – “Let Her Go”
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This acts as the backdoor pilot for Chicago P.D.
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2. Alternate Between Chicago Fire Season 2 and Chicago P.D. Season 1
When Chicago P.D. launched, it became tightly intertwined with Fire. Many early cases overlap.
Major Crossover:
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Chicago Fire Season 2, Episode 20 – “A Dark Day”
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Chicago P.D. Season 1, Episode 12 – “8:30 P.M.”
This two-parter marks the first major crossover and sets the tone for the shared universe.
3. The First SVU Crossovers and the Shay Storyline
By Season 3, Fire and P.D. begin crossing over more often.
Key Crossovers:
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Fire Season 3, Episode 7 – “Nobody Touches Anything” (introduces P.D. characters)
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Fire Season 3, Episode 13 – “Three Bells”
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P.D. Season 2, Episode 13 – “A Little Devil Complex”
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These connect through the emotional fallout from Leslie Shay’s death.
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Then came the first three-way crossover with Law & Order: SVU:
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P.D. Season 2, Episode 20 – “The Number of Rats”
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Fire Season 3, Episode 21 – “We Called Her Jellybean”
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SVU Season 16, Episode 20 – “Daydream Believer”
4. Enter Chicago Med
Chicago Med launched alongside Fire Season 4 and P.D. Season 3, expanding the universe into healthcare.
Backdoor Pilot:
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Fire Season 3, Episode 19 – “I Am the Apocalypse”
Crossover Highlight:
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Fire Season 4, Episode 10 – “The Beating Heart”
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Med Season 1, Episode 5 – “Malignant”
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When Herrmann is stabbed, all three shows unite in a race to save his life.
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P.D. Season 3, Episode 10 – “Now I’m God” also ties into this event through a connected medical case.
5. Chicago Justice Joins the Universe
Chicago Justice debuted in 2017, spinning out of a P.D. episode.
Backdoor Pilot:
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P.D. Season 3, Episode 21 – “Justice”
Four-Show Crossover Event:
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Fire Season 5, Episode 15 – “Deathtrap”
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P.D. Season 4, Episode 16 – “Emotional Proximity”
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Justice Season 1, Episode 1 – “Fake”
This dramatic three-part story revolves around a tragic club fire that claims the life of Lexi Olinsky.
6. Continue Alternating Through the Later Seasons
From this point, it’s best to follow the air dates of all three active shows — Fire, Med, and P.D. — as their storylines remain loosely aligned.
Notable Crossovers:
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Fire Season 7, Episode 2 – “Going to War”
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Med Season 4, Episode 2 – “When to Let Go”
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P.D. Season 6, Episode 2 – “Endings”
The “Infection” Event:
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Fire Season 8, Episode 4 – “Infection, Part I”
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Med Season 5, Episode 4 – “Infection, Part II”
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P.D. Season 7, Episode 4 – “Infection, Part III”
This crossover focuses on a deadly bacteria outbreak that unites the entire One Chicago team.
7. The Post-COVID Crossover: “In the Trenches”
The most recent multi-show event, In the Trenches, marked One Chicago’s triumphant return to crossover storytelling.
Episodes:
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Fire Season 13, Episode 11
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Med Season 10, Episode 11
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P.D. Season 12, Episode 11
The three-parter features a massive citywide disaster and some of the most emotional reunions in franchise history.
8. Optional: Law & Order: SVU Connections
For completionists, you can also include the SVU crossover episodes with Chicago P.D.:
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SVU Season 15, Episode 15 – “Comic Perversion” → P.D. Season 1, Episode 6 – “Conventions”
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SVU Season 17, Episode 14 – “Nationwide Manhunt” → P.D. Season 3, Episode 14 – “The Song of Gregory Williams Yates”
You don’t need to watch all of SVU, but these episodes enrich the wider One Chicago and Law & Order connection.
The Complete Watch Order Summary
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Chicago Fire Season 1 (Episodes 1–23)
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Chicago Fire Season 2 & Chicago P.D. Season 1 (Alternate episodes)
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Crossovers: “A Dark Day” / “8:30 P.M.”
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Chicago Fire Seasons 3–4
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Add Chicago P.D. Seasons 2–3
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Law & Order: SVU crossover episodes
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Introduce Chicago Med (from Fire 4×10 / Med 1×05 onward)
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Add Chicago Justice during Fire Season 5
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Alternate all three active shows (Fire, P.D., Med) from Season 6 onward
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Watch crossovers as listed (Infection, Going to War, In the Trenches)
