$72+ Flights from Ontario to St. Louis

One-way flight from Ontario to Lambert-St Louis

Highest demand for flights based on searches. 16% potential increase in price ($68 potential increase over avg. RT price).

Cheapest flight prices on average. 3% potential price decrease ($11 potential savings vs. average RT price).

Average for round-trip flights in July 2025

Find flight deals from Ontario to St. Louis

Cheapest flights from Ontario to St. Louis
Explore the most affordable flight options available from Ontario to St. Louis. Find the lowest fares from popular airlines and budget airlines, with prices last updated on July 3, 2025.

Fri 7/46:00 amONT - STL

1 stop5h 42mFrontier

Sat 7/57:29 pmSTL - ONT

1 stop6h 21mFrontier

Deal found 7/1

$172

Best flights from Ontario to St. Louis
Discover carefully curated flight deals from Ontario to St. Louis that have cost, travel time, and layovers in mind to ensure you get the best travel experience. Data last updated July 3, 2025.

Fri 9/58:59 pmONT - STL

1 stop10h 07mFrontier

Sun 9/710:39 amSTL - ONT

1 stop6h 45mFrontier

Deal found 7/2

$173

Last-minute flights from Ontario to St. Louis
Discover last-minute flight deals from Ontario to St. Louis. Data last updated July 3, 2025 and is based on user searches.

Fri 7/46:00 amONT - STL

1 stop5h 42mFrontier

Sat 7/57:29 pmSTL - ONT

1 stop6h 21mFrontier

Deal found 7/1

$172

Tue 7/85:15 pmONT - STL

2 stops13h 56mMultiple Airlines

Tue 7/156:41 amSTL - ONT

1 stop10h 05mMultiple Airlines

Deal found 7/1

$421

Tue 7/812:00 pmONT - STL

1 stop9h 59mHawaiian Airlines

Tue 7/156:41 amSTL - ONT

1 stop8h 46mHawaiian Airlines

Deal found 7/1

$617

Tue 7/85:05 amONT - STL

2 stops8h 42mUnited Airlines

Tue 7/155:15 amSTL - ONT

2 stops8h 59mUnited Airlines

Deal found 7/1

$628

Wed 7/912:00 pmONT - STL

1 stop9h 59mAlaska Airlines

Thu 7/106:41 amSTL - ONT

2 stops19h 18mAlaska Airlines

Deal found 7/2

$724

Wed 7/96:15 amONT - STL

2 stops8h 07mAmerican Airlines

Sun 7/137:03 amSTL - ONT

1 stop8h 44mAmerican Airlines

Deal found 7/2

$830

Thu 7/106:00 amONT - STL

1 stop5h 42mFrontier

Sun 7/132:27 pmSTL - ONT

1 stop8h 25mFrontier

Deal found 7/1

$214

Thu 7/105:59 pmONT - STL

2 stops12h 35mDelta

Thu 7/176:00 amSTL - ONT

1 stop6h 30mDelta

Deal found 7/1

$710

Sat 7/125:40 amONT - STL

2 stops9h 00mSouthwest

Mon 7/146:45 pmSTL - ONT

1 stop7h 10mSouthwest

Deal found 6/30

$623

One-way flights from Ontario to St. Louis
Search for one-way flight options from Ontario to St. Louis. Find affordable one-way fares based on user searches. Data last updated July 3, 2025.

Thu 7/246:00 amONT - STL

1 stop5h 42mFrontier

Deal found 7/2

$72

Tue 8/266:00 amONT - STL

1 stop9h 34mAlaska Airlines

Deal found 7/2

$159

Cheapflights Fare Finder

Use the filters below to find and compare flights from Ontario to St. Louis that are best for you.

Fly from

Fly to

Route

Depart

Return

Price

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 9/5

8:59 pm-9:06 am

1 stop10h 07m

Lambert-St Louis

Sun 9/7

10:39 am-3:24 pm

1 stop6h 45m

$173

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 7/10

6:00 am-1:42 pm

1 stop5h 42m

$72

Flights are sorted by cheapest round-trip flights first.

Deals found on 7/3

Best time to book a flight from Ontario to St. Louis

Have a flexible travel schedule? Discover the best time to fly to St. Louis from Ontario 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 Ontario to St. Louis

How far ahead should I book a flight from Ontario to St. Louis?

The best time to book flights from Ontario to St. Louis is 28 days before your desired departure date. The cost of your flight will likely increase significantly if you book two weeks in advance of your flight.

What is the cheapest month to book a flight from Ontario to St. Louis?

Currently, August is the cheapest month in which you can book a flight from Ontario to St. Louis (average of $311). Flying from Ontario to St. Louis in March is currently the most expensive (average of $356). 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 ONT to STL?

A simple way to save on the total cost of your ticket is to fly from Ontario to St. Louis in the afternoon. If you’re flexible enough to do this you can expect to save up to 60% on your trip compared to booking a flight at noon.

What is the cheapest day to fly from Ontario to St. Louis?

Travelers seeking maximum savings on their Ontario to St. Louis flight should consider departing on Wednesday at noon when fares are most often at their lowest. Monday afternoons flights should be avoided if possible as fares are typically the most expensive at this time.

Reviews of airlines servicing St. Louis

Get a feel of what it's like to fly with Alaska Airlines and Frontier from Ontario to St. Louis by reading reviews from past customers. Users have also rated airlines in terms of entertainment options, comfort, food, crew/service, and boarding process.

8.0

Very good

Reviews

1 / 20

10.0

Excellent

James,Apr 2025

LAX - SFO

Good flight except the uncontrollable cold air from the ceiling.

8.0

Very good

8.0

Very good

Reviews

1 / 20

10.0

Excellent

James,Apr 2025

LAX - SFO

Good flight except the uncontrollable cold air from the ceiling.

Frontier

5.9

Fair

3,286 reviews

8.0

Very good