AirHint found the following cheapest return flights from Ontario (ONT) to San Juan (SJU) in September 2025 (see full year).

Return flights

06 Sep - 13 Sep	jetBlue
11 Sep - 18 Sep	Southwest Airlines
11 Sep - 16 Sep	Southwest Airlines
02 Sep - 07 Sep	Southwest Airlines
10 Sep - 14 Sep	Southwest Airlines
05 Sep - 09 Sep	jetBlue
18 Sep - 22 Sep	jetBlue
11 Sep - 14 Sep	Southwest Airlines
05 Sep - 07 Sep	Southwest Airlines
28 Sep - 05 Oct	jetBlue
04 Sep - 08 Sep	Southwest Airlines
27 Sep - 07 Oct	Southwest Airlines

Also check the deals for one-way flights from Ontario to San Juan in September.

The deals are updated regularly. The prices may go up as tickets are purchased by other travellers. Only the cheapest flights are offered. Select a price to book and secure these cheap prices.

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Cheapest return flights from Ontario to San Juan in September from $437

Return flights