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

Return flights

08 Sep - 12 Sep	Delta
26 Sep - 03 Oct	Delta
20 Sep - 21 Sep	Frontier Airlines
21 Sep - 28 Sep	Frontier Airlines
18 Sep - 27 Sep	Frontier Airlines
04 Sep - 12 Sep	Frontier Airlines
27 Sep - 11 Oct	Frontier Airlines
04 Sep - 08 Sep	Frontier Airlines
05 Sep - 07 Sep	Frontier Airlines
06 Sep - 11 Sep	Frontier Airlines
04 Sep - 10 Sep	Frontier Airlines
05 Sep - 10 Sep	Frontier Airlines

Also check the deals for one-way flights from Chicago 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 Chicago to San Juan in September from 210€

Return flights