$40+ 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 3/18. Fares are subject to change and may not be available on all flights or dates of travel.
DEN — ORD
Feb 28 — Mar 71
1 adult, Economy
We work with more than 300 partners to bring you better travel deals
Find cheap flights from Colorado to Illinois with Cheapflights
1. Tell us where you want to go
Enter your travel information like dates, passengers, trip type (one-way or round trip), and preferred cabin class then click “Find deals”2. Select your favorite providers
We find the providers serving your travel needs. Choose up to four travel providers to compare side-by-side for flights, hotels, or car rentals.3. Compare prices and book
Review each provider’s pricing and select the best option for you! Book through your favorite provider’s website for a seamless experience.Cheap flight deals from Colorado to Illinois
Cheapest flights from Colorado to IllinoisExplore 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 January 29, 2026.
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 January 29, 2026.
This Super.com deal was found by Cheapflights users on 1/28. 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 Super.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 2/2010:01 am
DEN
- STL
Nonstop2h 08m
Frontier
Mon 2/231:54 pm
STL
- DEN
Nonstop2h 36m
Frontier
Deal found 1/28![Frontier logo]()
$79
This Frontier deal was found by Cheapflights users on 1/27. 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 2/63:38 pm
DEN
- STL
Nonstop2h 06m
Frontier
Sun 2/812:03 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 1/27![Frontier logo]()
$81
This Kiwi.com deal was found by Cheapflights users on 1/27. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 2/2810:48 am
DEN
- STL
Nonstop2h 08m
Frontier
Mon 3/28:22 pm
STL
- DEN
1 stop16h 34m
Frontier
Deal found 1/27![Frontier logo]()
$84
This Frontier deal was found by Cheapflights users on 1/28. 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.
Sat 3/146:35 am
DEN
- STL
Nonstop2h 14m
Frontier
Sat 3/218:12 pm
STL
- DEN
Nonstop2h 37m
Frontier
Deal found 1/28![Frontier logo]()
$85
This Super.com deal was found by Cheapflights users on 1/27. 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 Super.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 4/16:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Sat 4/48:16 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 1/27![Frontier logo]()
$87
This Frontier deal was found by Cheapflights users on 1/28. 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.
Sat 2/2110:48 am
DEN
- STL
Nonstop2h 08m
Frontier
Sat 2/282:51 pm
STL
- DEN
Nonstop2h 27m
Frontier
Deal found 1/28![Frontier logo]()
$88
This Frontier deal was found by Cheapflights users on 1/28. 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.
Sat 3/146:35 am
DEN
- STL
Nonstop2h 14m
Frontier
Fri 3/208:12 pm
STL
- DEN
Nonstop2h 37m
Frontier
Deal found 1/28![Frontier logo]()
$89
This Cheapflightsfares deal was found by Cheapflights users on 1/28. 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.
Wed 2/2512:48 pm
DEN
- STL
Nonstop2h 05m
Frontier
Wed 3/48:17 pm
STL
- DEN
1 stop12h 22m
Frontier
Deal found 1/28![Frontier logo]()
$92
This Cheapflightsfares deal was found by Cheapflights users on 1/27. 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 2/2110:48 am
DEN
- STL
Nonstop2h 08m
Frontier
Wed 2/254:51 pm
STL
- DEN
Nonstop2h 34m
Frontier
Deal found 1/27![Frontier logo]()
$93
This Orbitz deal was found by Cheapflights users on 1/26. 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 Orbitz is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 2/1110:50 am
DEN
- STL
Nonstop2h 08m
Frontier
Wed 2/188:17 pm
STL
- DEN
1 stop12h 22m
Frontier
Deal found 1/26![Frontier logo]()
$98
This Kiwi.com deal was found by Cheapflights users on 1/26. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 3/57:35 pm
DEN
- ORD
Nonstop2h 39m
Frontier
Tue 3/107:00 am
ORD
- DEN
1 stop12h 05m
Frontier
Deal found 1/26![Frontier logo]()
$114
This Kiwi.com deal was found by Cheapflights users on 1/26. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 3/48:54 am
DEN
- ORD
1 stop7h 09m
Frontier
Sun 3/810:53 am
ORD
- DEN
Nonstop2h 59m
Frontier
Deal found 1/26![Frontier logo]()
$115
Find flight deals from Colorado to Illinois
Keep the following information in mind while searching for Colorado to Illinois flight deals. Data was last updated January 29, 2026.
Most accurate provider | FlightHub 3 stars |
|---|---|
Most trusted provider | FlightHub 3 stars |
Round-trip from | $79 (Super.com) |
One-way from | $40 (Expedia) |
Popular in | November |
Cheapest in | February |
Average price | $212 |
Good round-trip deal | $227 or less |
Good one-way deal | $124 or less |
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 January 29, 2026.
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
Fri 2/20
10:01 am-1:09 pm
Nonstop2h 08m
Lambert-St Louis
Mon 2/23
8:47 pm-7:54 am
1 stop12h 07m
$114
DenverSt. Louis
DEN - STL
DENSTL
Denver Intl
Mon 3/23
6:35 am-9:49 am
Nonstop2h 14m
Lambert-St Louis
Fri 3/27
8:12 pm-9:49 pm
Nonstop2h 37m
$118
DenverSt. Louis
DEN - STL
DENSTL
Denver Intl
Wed 2/25
8:00 pm-6:51 am
2 stops33h 51m
Lambert-St Louis
Wed 3/4
5:18 pm-6:53 pm
Nonstop2h 35m
$123
DenverSt. Louis
DEN - STL
DENSTL
Denver Intl
Fri 2/20
10:01 am-1:09 pm
Nonstop2h 08m
Lambert-St Louis
Mon 2/23
8:22 pm-11:14 am
2 stops15h 52m
$139
DenverSt. Louis
DEN - STL
DENSTL
Denver Intl
Wed 2/11
10:29 pm-9:26 pm
1 stop21h 57m
Lambert-St Louis
Wed 2/18
8:17 pm-7:39 am
1 stop12h 22m
$144
DenverSt. Louis
DEN - STL
DENSTL
Denver Intl
Fri 2/27
11:49 am-12:27 am
2 stops11h 38m
Lambert-St Louis
Wed 3/4
5:18 pm-6:53 pm
Nonstop2h 35m
$156
DenverChicago
DEN - ORD
DENORD
Denver Intl
Thu 5/14
11:59 pm-2:17 pm
1 stop13h 18m
Chicago O'Hare Intl
Mon 5/18
5:16 pm-9:49 pm
1 stop29h 33m
$159
DenverSt. Louis
DEN - STL
DENSTL
Denver Intl
Sat 3/7
6:35 am-9:49 am
Nonstop2h 14m
Lambert-St Louis
Mon 3/9
7:47 am-9:34 pm
2 stops14h 47m
$162
DenverSt. Louis
DEN - STL
DENSTL
Denver Intl
Fri 3/13
6:35 am-9:49 am
Nonstop2h 14m
Lambert-St Louis
Sun 3/15
8:06 pm-3:56 am
1 stop8h 50m
$167
DenverChicago
DEN - ORD
DENORD
Denver Intl
Tue 3/3
8:30 pm-11:59 pm
Nonstop2h 29m
Chicago O'Hare Intl
Mon 3/9
8:40 am-10:33 am
Nonstop2h 53m
$185
Showing 1-10 of 60 results
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, July is the cheapest month in which you can book a flight from Colorado to Illinois (average of $46). Flying from Colorado to Illinois in June is currently the most expensive (average of $109). 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 January 29, 2026.
A simple way to save on the total cost of your ticket is to fly from Colorado to Illinois in the evening. If you’re flexible enough to do this you can expect to save up to 42% on your trip compared to booking a flight at noon.
What is the cheapest day to fly from Colorado to Illinois?
Use this chart to determine the cheapest time to fly round-trip from Colorado to Illinois. Price data was last updated on January 24, 2026.
Travelers seeking maximum savings on their Colorado to Illinois flight should consider departing on Friday at noon when fares are most often at their lowest. Sunday afternoons flights should be avoided if possible as fares are typically the most expensive at this time.
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 January 29, 2026.
The most flights from USCO to USIL are scheduled on a Thursday (45 on average). You will have fewer flight options on Saturday, which is when the least amount of flights are scheduled (25 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 January 29, 2026.
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.
Entertainment
7.5
Crew
8.6
Comfort
8.0
Overall
8.0
Boarding
8.1
Food
7.0
Reviews
1 / 20
2.0
MediocreThomas,Dec 2025
SEA - DEN
Entertainment
7.5
Crew
8.6
Comfort
8.0
Overall
8.0
Boarding
8.1
Food
7.0
Reviews
1 / 20
2.0
MediocreThomas,Dec 2025
SEA - DEN
Entertainment
7.5
Crew
8.6
Comfort
8.0
Overall
8.0
Boarding
8.1
Food
7.0
Reviews
1 / 20
2.0
MediocreThomas,Dec 2025
SEA - DEN
Entertainment
7.5
Crew
8.6
Comfort
8.0
Overall
8.0
Boarding
8.1
Food
7.0
Reviews
1 / 20
2.0
MediocreThomas,Dec 2025
SEA - DEN
Entertainment
7.5
Crew
8.6
Comfort
8.0
Overall
8.0
Boarding
8.1
Food
7.0
Reviews
1 / 20
2.0
MediocreThomas,Dec 2025
SEA - DEN
Entertainment
7.5
Crew
8.6
Comfort
8.0
Overall
8.0
Boarding
8.1
Food
7.0
Reviews
1 / 20
2.0
MediocreThomas,Dec 2025
SEA - DEN
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.
Browse thousands of different options on Cheapflights for your next trip
Toggle through the tabs below to find thousands of options on Cheapflights for your next trip.
Alternative routes for Colorado to Illinois
See prices for flight routes from nearby airports that may be better suited for you.
Top 6 airlines flying from Colorado to Illinois
Discover the top 6 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 January 29, 2026.
| Airline | Cheapest | Average | Flexibility | On-time |
|---|---|---|---|---|
| Cheapest$61 | Average$173 | FlexibilityNo cancel fee | On-time62% | |
| Cheapest$68 | Average$137 | FlexibilityNo cancel fee | On-time88% | |
| Cheapest$126 | Average$191 | FlexibilityNo cancel fee | On-time62% | |
| Cheapest$155 | Average$282 | FlexibilityNo cancel fee | On-time63% | |
| Cheapest$157 | Average$451 | FlexibilityNo cancel fee | On-time71% | |
| Cheapest$157 | Average$426 | FlexibilityNo cancel fee | On-time69% |