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

Return flights

27 Sep - 05 Oct	Frontier Airlines
03 Sep - 11 Sep	KLM
07 Sep - 14 Sep	Frontier Airlines
24 Sep - 30 Sep	Frontier Airlines
09 Sep - 23 Sep	Frontier Airlines
04 Sep - 11 Sep	Frontier Airlines
25 Sep - 02 Oct	Frontier Airlines
29 Sep - 14 Oct	Frontier Airlines
03 Sep - 18 Sep	Frontier Airlines
17 Sep - 08 Oct	Delta
09 Sep - 04 Oct	Frontier Airlines
02 Sep - 17 Sep	Delta
19 Sep - 11 Oct	Frontier Airlines
20 Sep - 08 Oct	Delta
17 Sep - 06 Oct	Delta
30 Sep - 07 Oct	Delta
05 Sep - 03 Oct	Delta
20 Sep - 27 Sep	Frontier Airlines
08 Sep - 15 Sep	Frontier Airlines
02 Sep - 27 Sep	Frontier Airlines

Also check the deals for one-way flights from Chicago to Istanbul 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 Istanbul in September from 607€

Return flights