In terms of precipitation, rainfall in Ontario ranges from 0.1 - 3.4 inches per month. February is typically the wettest month, when rainfall can reach 3.4 in. June is typically the driest time to visit Ontario when rainfall is around 0.1 in.

If weather is an important factor for your trip to Ontario, use this chart to help with planning. For those seeking warmer temperatures, August is the ideal time of year to visit, when temperatures reach an average of 78.8 F. Travelers looking to avoid the cold should look outside of December, when temperatures are typically at their lowest (around 53.6 F).

How far in advance should I book a flight from Islip, New York to Ontario?

When searching for a good deal, it’s best to be prepared for potential fluctuations in price. We recommend booking at least 31 days in advance, which can save you up to 83% on flights from Islip, New York to Ontario compared to booking the week you need them. Waiting 31 days out may not be for everyone, so we have options available for flights within the next two weeks, with the lowest price starting at $376. For sooner than that we have options available in the next 3 days from $598.

What is the cheapest month to fly from Islip, New York to Ontario?

September is one of the best times of the year to fly to Ontario from Islip, New York. Prices for September average $364 per person but you can even find prices for as low as $131. The most expensive prices can be found in the month of December. Opting for a September flight can save you 34% on your journey compared to booking in December

What is the cheapest time of day to fly from ISP to ONT?

When flying from Islip, New York to Ontario, the time of day you decide to fly out makes little to no difference towards the overall price you’ll pay on tickets.

Can I find deals for flights from Islip to Ontario that include hotel bookings?

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

How can I find direct flights from Islip to Ontario?

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

Can I find deals for business class flights from Islip to Ontario?

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

$250+ Flights from Islip, NY to Ontario

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Cheap flight deals from Islip to Ontario

Round-trip from	$410 (Frontier)
One-way from	$250 (Frontier)
Popular in	December
Cheapest in	September
Average price	$377

From Islip Long Island to Ontario

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One-way flight from Islip Long Island to Ontario

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Highest demand for flights based on searches. 7% potential increase in price ($30 potential increase over avg. RT price).

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Cheapest flight prices on average. 3% potential price decrease ($12 potential savings vs. average RT price).

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Average for round-trip flights in July 2025

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Find flight deals from Islip to Ontario

Cheapest flights from Islip to Ontario
Explore the most affordable flight options available from Islip to Ontario. Find the lowest fares from popular airlines and budget airlines, with prices last updated on July 16, 2025.

Tue 7/298:00 amISP - ONT

2 stops18h 50mFrontier

Tue 8/55:15 pmONT - ISP

2 stops19h 27mFrontier

Deal found 7/15

$410

Wed 9/1011:53 amISP - ONT

2 stops13h 37mMultiple Airlines

Tue 9/166:50 pmONT - ISP

2 stops15h 34mMultiple Airlines

Deal found 7/16

$891

Best flights from Islip to Ontario
Discover carefully curated flight deals from Islip to Ontario that have cost, travel time, and layovers in mind to ensure you get the best travel experience. Data last updated July 16, 2025.

Tue 7/298:00 amISP - ONT

2 stops18h 50mFrontier

Tue 8/55:15 pmONT - ISP

2 stops19h 27mFrontier

Deal found 7/15

$410

Wed 9/1011:53 amISP - ONT

2 stops13h 37mMultiple Airlines

Tue 9/166:50 pmONT - ISP

2 stops15h 34mMultiple Airlines

Deal found 7/16

$891

Last-minute flights from Islip to Ontario
Discover last-minute flight deals from Islip to Ontario. Data last updated July 16, 2025 and is based on user searches.

Sat 7/1911:53 amISP - ONT

2 stops12h 01mMultiple Airlines

Tue 7/226:28 pmONT - ISP

2 stops15h 56mMultiple Airlines

Deal found 7/16

$1,186

Thu 7/242:05 pmISP - ONT

2 stops22h 04mFrontier

Sun 7/275:21 pmONT - ISP

2 stops16h 43mFrontier

Deal found 7/14

$535

Tue 7/298:00 amISP - ONT

2 stops18h 50mFrontier

Tue 8/55:15 pmONT - ISP

2 stops19h 27mFrontier

Deal found 7/15

$410

One-way flights from Islip to Ontario
Search for one-way flight options from Islip to Ontario. Find affordable one-way fares based on user searches. Data last updated July 16, 2025.

Fri 8/229:58 amISP - ONT

2 stops11h 36mFrontier

Deal found 7/15

$250

Tue 8/267:30 amISP - ONT

2 stops13h 07mMultiple Airlines

Deal found 7/15

$446

Cheapflights Fare Finder

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

Fly from

Fly to

Route

Depart

Return

Price

IslipOntario

ISP - ONT

ISPONT

Islip Long Island

Tue 7/29

8:00 am-11:50 pm

2 stops18h 50m

Ontario

Tue 8/5

5:15 pm-3:42 pm

2 stops19h 27m

$410

IslipOntario

ISP - ONT

ISPONT

Islip Long Island

Wed 9/10

11:53 am-10:30 pm

2 stops13h 37m

Ontario

Tue 9/16

6:50 pm-1:24 pm

2 stops15h 34m

$891

IslipOntario

ISP - ONT

ISPONT

Islip Long Island

Fri 8/22

9:58 am-6:34 pm

2 stops11h 36m

$250

IslipOntario

ISP - ONT

ISPONT

Islip Long Island

Tue 8/26

7:30 am-5:37 pm

2 stops13h 07m

$446

Flights are sorted by cheapest round-trip flights first.

Deals found on 7/15

Best time to book a flight from Islip to Ontario

Have a flexible travel schedule? Discover the best time to fly to Ontario from Islip 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 Islip to Ontario

What is the cheapest month to book a flight from Islip, New York to Ontario?

Currently, August is the cheapest month in which you can book a flight from Islip, New York to Ontario (average of $246). Flying from Islip, New York to Ontario in March is currently the most expensive (average of $328). 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.

Reviews of airlines servicing Ontario

Peruse reviews from past customers who have flown with Frontier from Islip to Ontario to help guide your decision. You can also see how each airline stacks up in terms of entertainment options, comfort, food, crew/service, and boarding process.

Frontier

5.9

Fair

3,256 reviews

Reviews

1 / 20

8.0

Excellent

Anonymous,Jun 2025

TTN - TPA

TTN is a small airport for Frontier. Drop off is easy as is parking. The location is remote so there is zero traffic. The place could use a renovation but for the price you pay it is not necessary. Good-Staff is very friendly. Flight left on time. Bad- run down, deplaning/boarding on the tarmac. I got wet on the stairs outside of the plane while waiting to board.

Frontier

5.9

Fair

3,256 reviews

Frontier

5.9

Fair

3,256 reviews

Reviews

1 / 20

8.0

Excellent

Anonymous,Jun 2025

TTN - TPA

Related info for your journey

Can I find deals for flights from Islip to Ontario that include hotel bookings?
Yes. In addition to deals on Islip to Ontario flights, Cheapflights offers vacation packages that include both flights and hotel.
How can I find direct flights from Islip to Ontario?
After entering your origin and destination, apply the non-stop filter on the search result page to find direct flights from Islip to Ontario.
Can I find deals for business class flights from Islip to Ontario?
Yes. Cheapflights offers flight deals from Islip to Ontario 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 Islip, New York to Ontario?
Currently, August is the cheapest month in which you can book a flight from Islip, New York to Ontario (average of $246). Flying from Islip, New York to Ontario in March is currently the most expensive (average of $328). 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

Browse thousands of different options on Cheapflights for your next trip

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Complete your trip

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$250+ Cheap flights from Islip, NY to Ontario (ISP - ONT)

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 8/22. Fares are subject to change and may not be available on all flights or dates of travel.

Find cheap flights from Islip to Ontario with Cheapflights

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2. Select your favorite providers

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Cheap flight deals from Islip to Ontario

Round-trip from

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Popular in

Cheapest in

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Find flight deals from Islip to Ontario

Cheapest flights from Islip to OntarioExplore the most affordable flight options available from Islip to Ontario. Find the lowest fares from popular airlines and budget airlines, with prices last updated on July 16, 2025.

Explore the most affordable flight options available from Islip to Ontario. Find the lowest fares from popular airlines and budget airlines, with prices last updated on July 16, 2025.

Cheapflights Fare Finder

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

Best time to book a flight from Islip to Ontario

Have a flexible travel schedule? Discover the best time to fly to Ontario from Islip with our price prediction graph.

Cheapflights Insights

Everything you need to know about your flight from Islip to Ontario

What is the cheapest month to book a flight from Islip, New York to Ontario?

Reviews of airlines servicing Ontario

Peruse reviews from past customers who have flown with Frontier from Islip to Ontario to help guide your decision. You can also see how each airline stacks up in terms of entertainment options, comfort, food, crew/service, and boarding process.

Related info for your journey

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

Can I find deals for flights from Islip to Ontario that include hotel bookings?

How can I find direct flights from Islip to Ontario?

Can I find deals for business class flights from Islip to Ontario?

What is the cheapest month to book a flight from Islip, New York to Ontario?

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 Islip to Ontario

See prices for flight routes from nearby airports that may be better suited for you.

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Book with Flexibility

Travel Smart

Cheapest flights from Islip to Ontario
Explore the most affordable flight options available from Islip to Ontario. Find the lowest fares from popular airlines and budget airlines, with prices last updated on July 16, 2025.