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$64+ Cheap flights from Colorado to Illinois

This is the cheapest one-way flight price found by a Cheapflights user in the last 72 hours by searching for a flight departing on 11/16. Fares are subject to change and may not be available on all flights or dates of travel.
DEN — ORD
Aug 23 — Aug 301
Sat 8/23
Sat 8/30
1 adult, Economy
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Cheap flight deals from Colorado to Illinois

Keep the following information in mind while searching for Colorado to Illinois flight deals. Data was last updated August 18, 2025.

Round-trip from

$108
(Cheapflightsfares)

One-way from

$64
(Frontier)

Popular in

May

Cheapest in

October

Average price

$181

Good round-trip deal

$122 or less

Good one-way deal

$79 or less
From Colorado to Illinois
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One-way flight from Colorado to Illinois
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Highest demand for flights based on searches. 10% potential increase in price ($24 potential increase over avg. RT price).
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Cheapest flight prices on average. 1% potential price decrease ($3 potential savings vs. average RT price).
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Average for round-trip flights in August 2025
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Price to beat on a round-trip flight from Colorado to Illinois.
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Price to beat on a one-way flight from Colorado to Illinois.
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Find flight deals from Colorado to Illinois

Cheapest flights from Colorado to Illinois
Explore the most affordable flight options available from Colorado to Illinois. Find the lowest fares from popular airlines and budget airlines, with prices last updated on August 18, 2025.

This Mytrip deal was found by Cheapflights users on 8/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Mytrip is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 8/224:35 pmDEN - PIA
Nonstop2h 00mAllegiant Air
Mon 8/252:20 pmPIA - DEN
Nonstop2h 25mAllegiant Air
Deal found 8/16$99
This Cheapflightsfares deal was found by Cheapflights users on 8/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 8/306:00 amDEN - STL
Nonstop2h 11mFrontier
Tue 9/27:54 pmSTL - DEN
Nonstop2h 29mFrontier
Deal found 8/18$108
This Frontier deal was found by Cheapflights users on 8/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 9/26:00 amDEN - STL
Nonstop2h 11mFrontier
Thu 9/117:55 pmSTL - DEN
Nonstop2h 25mFrontier
Deal found 8/16$109
This Frontier deal was found by Cheapflights users on 8/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 9/296:00 amDEN - STL
Nonstop2h 06mFrontier
Wed 10/17:55 pmSTL - DEN
Nonstop2h 25mFrontier
Deal found 8/17$110
This Cheapflightsfares deal was found by Cheapflights users on 8/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 9/156:00 amDEN - STL
Nonstop2h 06mFrontier
Mon 9/227:55 pmSTL - DEN
Nonstop2h 25mFrontier
Deal found 8/18$112
This Cheapflightsfares deal was found by Cheapflights users on 8/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 9/256:00 amDEN - STL
Nonstop2h 06mFrontier
Mon 9/297:55 pmSTL - DEN
Nonstop2h 25mFrontier
Deal found 8/16$113
This Frontier deal was found by Cheapflights users on 8/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 9/266:00 amDEN - STL
Nonstop2h 06mFrontier
Sun 9/287:55 pmSTL - DEN
Nonstop2h 25mFrontier
Deal found 8/17$114
This Frontier deal was found by Cheapflights users on 8/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 10/306:00 amDEN - STL
Nonstop2h 07mFrontier
Sun 11/27:02 pmSTL - DEN
1 stop6h 15mFrontier
Deal found 8/17$115
This Cheapflightsfares deal was found by Cheapflights users on 8/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 9/186:00 amDEN - STL
Nonstop2h 06mFrontier
Mon 9/227:55 pmSTL - DEN
Nonstop2h 25mFrontier
Deal found 8/17$116
This Frontier deal was found by Cheapflights users on 8/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 11/78:44 pmDEN - ORD
Nonstop2h 31mFrontier
Sun 11/96:00 amORD - DEN
Nonstop2h 41mFrontier
Deal found 8/18$117
This Frontier deal was found by Cheapflights users on 8/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 9/188:30 pmDEN - ORD
Nonstop2h 29mFrontier
Mon 9/226:00 amORD - DEN
Nonstop2h 45mFrontier
Deal found 8/18$118
This Frontier deal was found by Cheapflights users on 8/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sun 9/286:00 amDEN - STL
Nonstop2h 06mFrontier
Wed 10/17:55 pmSTL - DEN
Nonstop2h 25mFrontier
Deal found 8/17$118

Cheapflights Fare Finder

 
Customize your flight search to find flights from Colorado to Illinois that fit within your specific budget. Explore options based on user searches and filter the results based on your desired price range. Find flights that match your budget for a cost-effective journey. Over the last 7 days, Cheapflights users made 2,558,603 searches. Data last updated August 18, 2025.
Use the filters below to find and compare flights from Colorado to Illinois that are best for you.

Fly from

Colorado

Fly to

Illinois

Route

Depart

Return

Price

DenverSt. Louis

DEN - STL

DENSTL

Denver Intl

Sat 8/30

6:00 am-9:11 am

Nonstop2h 11m

Lambert-St Louis

Tue 9/2

7:54 pm-9:23 pm

Nonstop2h 29m

$108

DenverSt. Louis

DEN - STL

DENSTL

Denver Intl

Sun 10/12

6:00 am-9:07 am

Nonstop2h 07m

Lambert-St Louis

Tue 10/14

7:52 pm-9:20 pm

Nonstop2h 28m

$109

DenverSt. Louis

DEN - STL

DENSTL

Denver Intl

Sun 9/21

6:00 am-9:06 am

Nonstop2h 06m

Lambert-St Louis

Wed 9/24

7:55 pm-9:20 pm

Nonstop2h 25m

$109

DenverSt. Louis

DEN - STL

DENSTL

Denver Intl

Tue 9/2

6:00 am-9:11 am

Nonstop2h 11m

Lambert-St Louis

Thu 9/11

7:55 pm-9:20 pm

Nonstop2h 25m

$109

DenverSt. Louis

DEN - STL

DENSTL

Denver Intl

Mon 9/29

6:00 am-9:06 am

Nonstop2h 06m

Lambert-St Louis

Wed 10/1

7:55 pm-9:20 pm

Nonstop2h 25m

$110

DenverSt. Louis

DEN - STL

DENSTL

Denver Intl

Thu 10/30

6:00 am-9:07 am

Nonstop2h 07m

Lambert-St Louis

Sun 11/2

7:02 pm-12:17 am

1 stop6h 15m

$112

DenverSt. Louis

DEN - STL

DENSTL

Denver Intl

Mon 9/15

6:00 am-9:06 am

Nonstop2h 06m

Lambert-St Louis

Mon 9/22

7:55 pm-9:20 pm

Nonstop2h 25m

$112

DenverSt. Louis

DEN - STL

DENSTL

Denver Intl

Sat 11/1

6:00 am-9:07 am

Nonstop2h 07m

Lambert-St Louis

Sun 11/2

7:02 pm-12:17 am

1 stop6h 15m

$113

DenverSt. Louis

DEN - STL

DENSTL

Denver Intl

Thu 9/25

6:00 am-9:06 am

Nonstop2h 06m

Lambert-St Louis

Mon 9/29

7:55 pm-9:20 pm

Nonstop2h 25m

$113

DenverSt. Louis

DEN - STL

DENSTL

Denver Intl

Fri 10/31

6:00 am-9:07 am

Nonstop2h 07m

Lambert-St Louis

Sun 11/2

7:02 pm-12:17 am

1 stop6h 15m

$113

Flights are sorted by cheapest round-trip flights first.

Deals found on 8/18

Showing 1-10 of 60 results
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Best time to book a flight from Colorado to Illinois

Have a flexible travel schedule? Discover the best time to fly to Illinois from Colorado with our price prediction graph.
Estimated round-trip price
Rates are based on past data. Find the cheapest month and day to book your flight based on your travel requirements, then search for cheap deals.

Cheapflights Insights

Everything you need to know about your flight from Colorado to Illinois

What is the cheapest month to book a flight from Colorado to Illinois?

Currently, August is the cheapest month in which you can book a flight from Colorado to Illinois (average of $245). Flying from Colorado to Illinois in March is currently the most expensive (average of $321). There are several factors that can impact the price of a flight, so comparing airlines, departure airports and flight times can provide users with more options.

What is the cheapest time of day to fly from CO to IL?

Find hourly flight availability from Colorado to Illinois. Discover flight options and departure times throughout the day, allowing you to choose a departure time that suits your schedule. Data last updated August 18, 2025.

Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Colorado to Illinois as you normally would.

Weekly flight availability from Colorado to Illinois

Explore weekly flight availability from Colorado to Illinois. Discover flights operating on different days of the week, giving you the flexibility to choose a travel day that best fits your plans. Compare info to find the most convenient option for your journey. Data last updated August 18, 2025.

The most flights from USCO to USIL are scheduled on a Monday (65 on average). You will have fewer flight options on Wednesday, which is when the least amount of flights are scheduled (27 on average).

Reviews of airlines servicing Illinois

Get insights into the airlines that provide service to Illinois. Read reviews, discover amenities, and learn about the overall travel experience offered by airlines. Use this information to make informed decisions when choosing an airline for your flight to Illinois. Reviews last updated August 18, 2025.
Read reviews from past customers who have flown Southwest, United Airlines, and American Airlines from Colorado to Illinois. You can also see how each airline compares in terms of entertainment options, comfort, food, crew/service, and boarding process.
Southwest
8.0
Very good
4,246 reviews

Comfort

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Overall

8.0

Boarding

8.1

Reviews

1 / 20
8.0
Excellent

Walter,Aug 2025

OAK - SAN

Dozens of flights and I've never seen a row's beverages forgotten. I even went back and asked the attendant to check on them and nothing. I really hope it didn't have something to do with the Black mother with her kid in the row. Otherwise it was a typical Southwest flight, rapid boarding, tolerable leg room.
Southwest
8.0
Very good
4,246 reviews
Southwest
8.0
Very good
4,246 reviews

Comfort

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Overall

8.0

Boarding

8.1

Reviews

1 / 20
8.0
Excellent

Walter,Aug 2025

OAK - SAN

Dozens of flights and I've never seen a row's beverages forgotten. I even went back and asked the attendant to check on them and nothing. I really hope it didn't have something to do with the Black mother with her kid in the row. Otherwise it was a typical Southwest flight, rapid boarding, tolerable leg room.
United Airlines
7.4
Good
8,925 reviews
Southwest
8.0
Very good
4,246 reviews

Comfort

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Overall

8.0

Boarding

8.1

Reviews

1 / 20
8.0
Excellent

Walter,Aug 2025

OAK - SAN

Dozens of flights and I've never seen a row's beverages forgotten. I even went back and asked the attendant to check on them and nothing. I really hope it didn't have something to do with the Black mother with her kid in the row. Otherwise it was a typical Southwest flight, rapid boarding, tolerable leg room.
American Airlines
7.2
Good
10,000 reviews
Southwest
8.0
Very good
4,246 reviews

Comfort

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Overall

8.0

Boarding

8.1

Reviews

1 / 20
8.0
Excellent

Walter,Aug 2025

OAK - SAN

Dozens of flights and I've never seen a row's beverages forgotten. I even went back and asked the attendant to check on them and nothing. I really hope it didn't have something to do with the Black mother with her kid in the row. Otherwise it was a typical Southwest flight, rapid boarding, tolerable leg room.
Allegiant Air
7.2
Good
701 reviews
Southwest
8.0
Very good
4,246 reviews

Comfort

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Overall

8.0

Boarding

8.1

Reviews

1 / 20
8.0
Excellent

Walter,Aug 2025

OAK - SAN

Dozens of flights and I've never seen a row's beverages forgotten. I even went back and asked the attendant to check on them and nothing. I really hope it didn't have something to do with the Black mother with her kid in the row. Otherwise it was a typical Southwest flight, rapid boarding, tolerable leg room.
Frontier
5.8
Fair
3,212 reviews
Southwest
8.0
Very good
4,246 reviews

Comfort

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Overall

8.0

Boarding

8.1

Reviews

1 / 20
8.0
Excellent

Walter,Aug 2025

OAK - SAN

Dozens of flights and I've never seen a row's beverages forgotten. I even went back and asked the attendant to check on them and nothing. I really hope it didn't have something to do with the Black mother with her kid in the row. Otherwise it was a typical Southwest flight, rapid boarding, tolerable leg room.

Related info for your journey

Find useful and relevant information for your journey from Colorado to Illinois. Access travel guides, tips, and recommendations to enhance your travel experience. Get information about local attractions, weather, transportation options, and more.

  • How long is the flight from Colorado to Illinois?

    Airlines like Frontier, Allegiant Air, and United Airlines fly from Colorado to Illinois in about 1h 51m. The time it takes to get you to your destination is usually consistent. Colorado and Illinois are separated by a distance of 790 mi. Most flights are nonstop.

  • What are the cheapest airlines to fly from Colorado to Illinois one-way?

    The cheapest airline one-way is Frontier, with whom users have recently found tickets for as low as $64. However, be on the lookout for offers from Southwest and United Airlines, as they are both options that can get you from Colorado to Illinois for a low price.

  • Can I find deals for flights from Colorado to Illinois that include hotel bookings?

    Yes. In addition to deals on Colorado to Illinois flights, Cheapflights offers vacation packages that include both flights and hotel.

  • How can I find direct flights from Colorado to Illinois?

    After entering your origin and destination, apply the non-stop filter on the search result page to find direct flights from Colorado to Illinois.

  • Can I find deals for business class flights from Colorado to Illinois?

    Yes. Cheapflights offers flight deals from Colorado to Illinois by cabin class. In addition to browsing deals, you can also filter by cabin class on the search results page after making a search.

  • What is the cheapest month to book a flight from Colorado to Illinois?

    Currently, August is the cheapest month in which you can book a flight from Colorado to Illinois (average of $245). Flying from Colorado to Illinois in March is currently the most expensive (average of $321). There are several factors that can impact the price of a flight, so comparing airlines, departure airports and flight times can provide users with more options.

See more FAQs

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Alternative routes for Colorado to Illinois

See prices for flight routes from nearby airports that may be better suited for you.
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Top 5 airlines flying from Colorado to Illinois

Discover the top 5 airlines that operate flights from Colorado to Illinois. Compare their services, reliability, and customer satisfaction ratings to choose the airline that best suits your travel preferences and needs. Over the last 7 days, Cheapflights users made 2,558,603 searches. Data last updated August 18, 2025.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$57Average$161FlexibilityNo cancel feeOn-time62%
Allegiant AirCheapest$84Average$159FlexibilityNo cancel feeOn-time88%
SouthwestCheapest$153Average$290FlexibilityNo cancel feeOn-time63%
American AirlinesCheapest$154Average$413FlexibilityNo cancel feeOn-time71%
United AirlinesCheapest$165Average$438FlexibilityNo cancel feeOn-time69%

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