Gateway Arch in St. Louis Missouri, America, USA.

$105 Cheap Flights from Islip (ISP) to St. Louis (STL)

View $105 flight on Tue, Sep 1, 2026Opens in a new window

Popular airlines from MacArthur Airport (ISP) to St. Louis Lambert Intl. Airport (STL)

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Cheap Flights from Islip to St. Louis (ISP-STL)

Prices were available within the past 7 days and start at $105 for one-way flights and $247 for round trip, for the period specified. Prices and availability are subject to change. Additional terms apply.

Southwest Airlines
Tue, Jul 14 - Tue, Jul 28
ISP
Islip
STL
St. Louis
$247 Roundtrip, found 3 days ago
$247
Roundtrip
found 3 days ago
Select Southwest Airlines flight, departing Tue, Jul 14 from Islip to St. Louis, returning Tue, Jul 28, priced at $247 found 3 days ago
Southwest Airlines
Tue, Jul 14 - Tue, Jul 28
ISP
Islip
STL
St. Louis
$252 Roundtrip, found 3 days ago
$252
Roundtrip
found 3 days ago
Select Southwest Airlines flight, departing Tue, Jul 14 from Islip to St. Louis, returning Tue, Jul 28, priced at $252 found 3 days ago
Southwest Airlines
Tue, Jul 14 - Tue, Jul 28
ISP
Islip
STL
St. Louis
$257 Roundtrip, found 3 days ago
$257
Roundtrip
found 3 days ago
Select Southwest Airlines flight, departing Tue, Jul 14 from Islip to St. Louis, returning Tue, Jul 28, priced at $257 found 3 days ago
Southwest Airlines
Tue, Jul 14 - Tue, Jul 28
ISP
Islip
STL
St. Louis
$263 Roundtrip, found 3 days ago
$263
Roundtrip
found 3 days ago
Select Southwest Airlines flight, departing Tue, Jul 14 from Islip to St. Louis, returning Tue, Jul 28, priced at $263 found 3 days ago
Southwest Airlines
Mon, Sep 28 - Wed, Sep 30
ISP
Islip
STL
St. Louis
$273 Roundtrip, found 1 day ago
$273
Roundtrip
found 1 day ago
Select Southwest Airlines flight, departing Mon, Sep 28 from Islip to St. Louis, returning Wed, Sep 30, priced at $273 found 1 day ago
Southwest Airlines
Sat, Sep 12 - Sun, Sep 13
ISP
Islip
STL
St. Louis
$277 Roundtrip, found 8 hours ago
$277
Roundtrip
found 8 hours ago
Select Southwest Airlines flight, departing Sat, Sep 12 from Islip to St. Louis, returning Sun, Sep 13, priced at $277 found 8 hours ago
Southwest Airlines
Mon, Sep 28 - Wed, Sep 30
ISP
Islip
STL
St. Louis
$278 Roundtrip, found 1 day ago
$278
Roundtrip
found 1 day ago
Select Southwest Airlines flight, departing Mon, Sep 28 from Islip to St. Louis, returning Wed, Sep 30, priced at $278 found 1 day ago
Southwest Airlines
Tue, Jul 14 - Tue, Jul 28
ISP
Islip
STL
St. Louis
$280 Roundtrip, found 3 days ago
$280
Roundtrip
found 3 days ago
Select Southwest Airlines flight, departing Tue, Jul 14 from Islip to St. Louis, returning Tue, Jul 28, priced at $280 found 3 days ago
Southwest Airlines
Sat, Sep 12 - Sun, Sep 13
ISP
Islip
STL
St. Louis
$283 Roundtrip, found 8 hours ago
$283
Roundtrip
found 8 hours ago
Select Southwest Airlines flight, departing Sat, Sep 12 from Islip to St. Louis, returning Sun, Sep 13, priced at $283 found 8 hours ago
Southwest Airlines
Tue, Jul 14 - Tue, Jul 28
ISP
Islip
STL
St. Louis
$285 Roundtrip, found 3 days ago
$285
Roundtrip
found 3 days ago
Select Southwest Airlines flight, departing Tue, Jul 14 from Islip to St. Louis, returning Tue, Jul 28, priced at $285 found 3 days ago

Frequently asked questions

How much does a flight from Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.) cost?
You can find cheap one-way flights from $105 and cheap return flights from $247 Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.) with Expedia. One-way flights usually range from $284 to $1482, and return flights typically cost between $306 and $1478. Flight prices vary based on the month and day of the week you want to travel, as well as the airline and how far in advance you book your ticket. Filter your search on Expedia by "Price (lowest to highest)" to see the cheapest fares first, and use the Price Tracking tool to receive alerts when Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.) ticket fares go up or down.*Typical price ranges based on flights available on Expedia in the last year. Prices include multi-airline options.
What is the cheapest month to fly from Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.)?
The cheapest month to fly from ISP to STL is July when demand is low. Traveling in off-peak or shoulder months is usually a good way to secure cheap tickets, just remember to avoid flying during holidays if you're able to. Use the calendar view in your search to see which months have low fares on this route.
Which airlines fly direct from Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.)?
Enter ISP to STL and your travel dates, then apply the 'Nonstop' filter to see only direct flights.
What is the cheapest airline that flies from Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.)?
Frontier Airlines is one of the cheapest airlines offering connecting flights from MacArthur (ISP) to Lambert-St. Louis Intl. (STL), with round-trip tickets starting from around $342. This option allows you to travel conveniently while keeping your budget in check. Use Expedia's search tool to compare the prices and schedules of airlines that fly this route to find the best option for your plans and budget.*Prices based on flights available on Expedia in the last year.
How do I find cheap flights from Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.)?
To find a cheap flight from Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.), be flexible with your dates. Traveling outside of peak vacation months and booking a mid-week flight can help you save. Early morning and late night flights are often more affordable, too. Expedia allows you to compare flight times, airlines and routes all in one place to find low fares. You can also set up Price Tracking and receive alerts when fares go up or down.
What is the best time to fly from Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.)?
The best time to fly is usually mid-week (Tuesday or Wednesday) and during early morning hours as flights tend to be cheaper, less crowded, and generally more on-time. Avoid major holidays and peak vacation seasons for smoother travel. Combining off-peak days and hours often gives the best combination of cost, comfort, and convenience.
What is the earliest flight from Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.)?
The earliest flight from Islip, NY (ISP) to St. Louis, MO (STL) typically departs at around 5:00 AM local time, operated by Southwest Airlines. This seasonal service is available in April and May, allowing you to maximize your time in St. Louis. To compare early flights on Expedia, select the "Early Morning" and "Morning" filters in your search.
What are the most popular departure times for flights from Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.)?
The most popular departure times for flights from Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.) are in the late afternoon to early evening, from 3pm to 6pm. About 32% of passengers prefer this time window. Many major carriers, including Southwest Airlines, offer flights during this window. This timing works well because it allows you to travel after a productive day.
How long does it take to fly from Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.)?
Flights from ISP to STL with one stop typically take around 8 hours, covering approximately 926 miles. Keep in mind that actual flight times can vary due to wind patterns, weather, and air traffic.
Can you fly business or first class from Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.)?
Select the "Business class" and "First class" filters when looking for ISP to STL flights on Expedia. This is the easiest way to compare prices, routes and flight times for your trip.
How do I earn miles on a Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.) flight with Expedia?
It's easy to earn miles on a Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.) flight when you book with Expedia. Before you confirm your booking, simply select your frequent flyer program and enter your program number. As a member of One Key™, you can also earn OneKeyCash™* on top of your airline miles when you book with Expedia.*Excludes taxes and fees. OneKeyCash is not redeemable for cash and can only be used on Expedia and other participating brands.
What airports do you fly into for St. Louis from MacArthur (ISP)?
From MacArthur (ISP), you can fly into Lambert-St. Louis Intl. (STL) to reach St. Louis. Some flights may connect through major hubs like Logan Intl. (BOS), Baltimore Washington Intl. Thurgood Marshall (BWI), Orlando Intl. (MCO) before reaching St. Louis. Compare routes and airports on Expedia to find the best flight options for your travel plans.
Is it cheaper to buy a plane ticket from Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.) at the last minute?
Typically, booking a last minute flight from Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.) will be more expensive than booking in advance. As the departure date approaches, there are usually fewer seats available which can drive up the cost. However, if there's some wiggle room with your travel dates and times, you could bag a cheap last-minute fare.
Is it cheaper to book a Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.) flight and hotel package?
Securing a Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.) St Louis Vacation Packages is usually cheaper than booking separately. With Expedia, you can enjoy the ease of organizing your travels all in one place. Select from our extensive range of stays and then add flights, activities and car rentals to your booking. Bundle everything together, and you could save hundreds of dollars.
Can I cancel or change the date of my flight from Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.)?
If you booked your Islip, NY (ISP-MacArthur) to St. Louis, MO (STL-Lambert-St. Louis Intl.) flight within the last 24 hours, you may be able to modify or cancel it without any fees. Depending on the airline and the type of ticket you have, additional charges may apply for changes beyond this timeframe. Airline policies and contact information can be found in your itinerary or confirmation email. Or, head to our Customer Service portal if you'd like more information.

Travel information

Origin airport
MacArthur
Destination airport
Lambert-St. Louis Intl.
Airlines serving
Southwest Airlines
Roundtrip price
$246
Distance
926 mi

Book with confidence

Islip to St. Louis Flights

The cheapest times to fly from Islip to St. Louis

On average, Thursday can be the cheapest time to fly, according to data from the Airlines Reporting Corporation (ARC), one of the world's biggest databases for global airline sales. The data reveals that you could save up to 16% by flying on a Thursday—the cheapest day to travel on average—instead of a Sunday—the most expensive. Some of the most affordable flights from Islip to St. Louis are during the month of July. You can find some of the cheapest flights from Islip to St. Louis with Expedia's search tool and vast selection of airlines.

 

The best time to book a flight from Islip to St. Louis

Sunday is one of the best days to book for cheap flights from Islip to St. Louis: Tickets reserved on a Sunday cost between 6% and 13% less than those reserved on a Friday, according to ARC data. The data also suggests booking early can also lead to cheaper airfares. You could save 24% by buying your tickets for domestic flights at least a month in advance and 10% by booking international flights 2 months in advance.

 

How to find cheap round-trip tickets from Islip to St. Louis

Being flexible with your dates and using Expedia's Price Drop Protection and Price Tracking features are some of the best ways of finding a cheap ticket from Islip to St. Louis in 2026. You can also book with separate airlines for your outbound and return journeys, from $105 one-way. Expedia also offers Price Drop Protection, so if the cost of your airfare goes down after booking, you'll receive a credit for the difference*. This is available for a small fee, and is free to One Key Gold and Platinum tier members.

 

Expedia's Price Tracking feature means you can stay on top of airfares without manually checking every day. It sends you automated price alerts for cheap Islip to St. Louis flights and uses historical data to indicate when the best time to book is. Download Expedia's free app to activate this handy tool in a few easy taps.

 

You could also save big by booking one of Expedia's vacation packages. Bundling together your Islip to St. Louis airfare with your accommodations and car rental is often cheaper than booking everything separately. There’s also One Key, Expedia's generous rewards program. Join for free and you could earn One Key cash on most bookings to save on future adventures.

 

*Terms apply.

 

Disclaimer: ARC The statistics are based on average round-trip ticket prices between January and August 2023. The percentages you see are averages.

 

Islip to St. Louis Flights

*Flight schedules are subject to change.

*Available to One Key members.

 

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