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

Return flights

25 Sep - 30 Sep	United
26 Sep - 30 Sep	United
07 Sep - 13 Sep	Southwest Airlines
17 Sep - 20 Sep	Southwest Airlines
30 Sep - 05 Oct	Southwest Airlines
18 Sep - 21 Sep	Southwest Airlines
22 Sep - 29 Sep	Southwest Airlines
19 Sep - 22 Sep	Southwest Airlines
09 Sep - 16 Sep	Southwest Airlines
25 Sep - 29 Sep	Southwest Airlines
05 Sep - 07 Sep	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 288€

Return flights