$108 Cheap Frontier Airlines flights St. Louis (STL) to Ontario (ONT)

View $108 flight on Wed, Aug 27, 2025Opens in a new window

  • Plan, book, fly with confidence

  • trending down icon
    Be in the know
    Get alerts if flight prices drop or rise*
  • bex rewards loyalty icon
    Book smarter
    Save up to 30% on select hotels after you book a flight*
  • one key icon
    Earn twice
    Earn your airline miles on top of our OneKeyCash
    Learn about One Key

$108 Cheap Frontier Airlines flights St. Louis (STL) to Ontario (ONT)

Prices were available within the past 7 days and start at $108 for one-way flights and $200 for round trip, for the period specified. Prices and availability are subject to change. Additional terms apply.

Frontier Airlines
Thu, Sep 11 - Mon, Sep 15
STL
St. Louis
ONT
Ontario
$200 Roundtrip, found 1 day ago
$200
Roundtrip
found 1 day ago
Select Frontier Airlines flight, departing Thu, Sep 11 from St. Louis to Ontario, returning Mon, Sep 15, priced at $200 found 1 day ago
Frontier Airlines
Thu, Aug 21 - Mon, Aug 25
STL
St. Louis
ONT
Ontario
$205 Roundtrip, found 19 hours ago
$205
Roundtrip
found 19 hours ago
Select Frontier Airlines flight, departing Thu, Aug 21 from St. Louis to Ontario, returning Mon, Aug 25, priced at $205 found 19 hours ago
Frontier Airlines
Sat, Aug 23 - Sat, Aug 30
STL
St. Louis
ONT
Ontario
$216 Roundtrip, found 1 day ago
$216
Roundtrip
found 1 day ago
Select Frontier Airlines flight, departing Sat, Aug 23 from St. Louis to Ontario, returning Sat, Aug 30, priced at $216 found 1 day ago
Frontier Airlines
Wed, Sep 10 - Sat, Sep 27
STL
St. Louis
ONT
Ontario
$220 Roundtrip, found 6 days ago
$220
Roundtrip
found 6 days ago
Select Frontier Airlines flight, departing Wed, Sep 10 from St. Louis to Ontario, returning Sat, Sep 27, priced at $220 found 6 days ago
Frontier Airlines
Thu, Sep 4 - Sun, Sep 7
STL
St. Louis
ONT
Ontario
$220 Roundtrip, found 19 hours ago
$220
Roundtrip
found 19 hours ago
Select Frontier Airlines flight, departing Thu, Sep 4 from St. Louis to Ontario, returning Sun, Sep 7, priced at $220 found 19 hours ago
Frontier Airlines
Sat, Nov 1 - Wed, Nov 5
STL
St. Louis
ONT
Ontario
$225 Roundtrip, found 1 day ago
$225
Roundtrip
found 1 day ago
Select Frontier Airlines flight, departing Sat, Nov 1 from St. Louis to Ontario, returning Wed, Nov 5, priced at $225 found 1 day ago
0
Flights from St. Louis (STL) to Ontario (ONT)
Origin airport
Lambert-St. Louis Intl.
Destination airport
Los Angeles - Ontario Intl.
Airlines serving
Alaska Airlines, American Airlines, Delta, Frontier Airlines, Hawaiian Airlines, Southwest Airlines, United
Popular airline
Delta
Distance
1541 mi

Frequently asked questions

How much is a Frontier Airlines flight from Lambert-St. Louis Intl. Airport (STL) to Los Angeles - Ontario Intl. Airport (ONT)?
Make use of the "Price (lowest to highest)" filter on Expedia to find cheap Frontier Airlines round-trip flights from $200 from STL to ONT. Affordable one-way tickets from $108 are also available.**These prices were available on Expedia within the past 7 days, for flights departing within the next year. Prices and availability are subject to change. Additional terms apply.
What is the cheapest month to fly from STL to ONT with Frontier Airlines?
January is one of the cheapest months to jet off to Ontario with Frontier Airlines. You could also find great deals on one-way and round-trip fares in April.
What is the cheapest time to book flights from Lambert-St. Louis Intl. Airport (STL) to Los Angeles - Ontario Intl. Airport (ONT) with Frontier Airlines?
Look for cheap Frontier Airlines flights from Lambert-St. Louis Intl. Airport (STL) to Los Angeles - Ontario Intl. Airport (ONT) one to three months before your departure day. Travelers who book domestic flights 34 to 86 days in advance can save 25% compared to those who book just 6 to 12 days ahead. No matter the fare type and itinerary, the ideal day to book a domestic flight is usually Sunday and the most expensive day is typically Monday. Passengers who book on a Sunday can save 6% on average compared to those who book their travel on a Monday.**Ideal booking window recommendation is based on average round-trip ticket prices for January through November for 2024. Best day of the week to book recommendation is based on average round-trip ticket prices for January through October 2024. All data sourced from ARC's global airline sales database.
Does Frontier Airlines fly nonstop from Lambert-St. Louis Intl. Airport (STL) to Los Angeles - Ontario Intl. Airport (ONT)?
Select our "Nonstop" filter when searching for direct Frontier Airlines flights from STL to ONT. It's also a great way to compare other carriers offering the same direct trip.
What is the earliest Frontier Airlines flight from STL to ONT?
Browse Frontier Airlines's earliest flights from STL to ONT by selecting our "Early Morning" and "Morning" filters. Not only will you get to your destination sooner, early departures also experience 20% fewer cancellations.**Most reliable time of the day recommendation is based on January through August 2024 flight status data sourced from OAG's global flight data platform.
What airports does Frontier Airlines fly into in Ontario?
Frontier Airlines flights from Lambert-St. Louis Intl. Airport (STL) to Ontario come in to Los Angeles - Ontario Intl. Airport (ONT). This is the main entry point to this destination.
Why fly with Frontier Airlines from STL to ONT?
A rewarding loyalty program and the chance to rack up points through Frontier Miles are the start of the reasons to jet off from STL to ONT with Frontier Airlines. Plus, when you sign up to our One Key™ program, you can receive OneKeyCash™* on top of Frontier Airlines's loyalty program earnings. You can put it toward your future trips.*OneKeyCash™ disclaimer - OneKeyCash™ is not redeemable for cash and can only be used on Expedia, Hotels.com and Vrbo.
Can I change or cancel my Frontier Airlines flight from Lambert-St. Louis Intl. Airport (STL) to Los Angeles - Ontario Intl. Airport (ONT)?
Changes are typically free within 24 hours of making a booking, but your airline may charge a fee after that time. For more information about altering your reservation, head to your "Trips," select your flight and click on "Manage Booking." If you want the freedom to change your plans without being charged, check the "Changes included" or "No cancel fee" filter when planning your next getaway.

Explore a world of travel with Expedia

*Available to One Key members.