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

Return flights

28 Sep - 05 Oct	United
02 Sep - 25 Sep	Southwest Airlines
17 Sep - 23 Sep	Southwest Airlines
10 Sep - 14 Sep	Southwest Airlines
16 Sep - 21 Sep	Southwest Airlines
01 Sep - 14 Sep	Southwest Airlines
13 Sep - 15 Sep	Southwest Airlines
18 Sep - 23 Sep	Southwest Airlines
11 Sep - 15 Sep	Southwest Airlines
13 Sep - 21 Sep	Southwest Airlines
26 Sep - 05 Oct	Southwest Airlines
02 Sep - 07 Sep	Southwest Airlines
28 Sep - 12 Oct	Southwest Airlines

Also check the deals for one-way flights from Ontario to San Jose 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 Jose in September from 322€

Return flights