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

Return flights

11 Sep - 18 Sep	Frontier Airlines
19 Sep - 25 Sep	Frontier Airlines
25 Sep - 28 Sep	Frontier Airlines
08 Sep - 14 Sep	Frontier Airlines
08 Sep - 22 Sep	Frontier Airlines
10 Sep - 17 Sep	Delta
09 Sep - 16 Sep	Delta
08 Sep - 30 Sep	Delta
30 Sep - 10 Oct	Delta
13 Sep - 27 Sep	Delta
20 Sep - 03 Oct	Delta

Also check the deals for one-way flights from Chicago to Seoul 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 Seoul in September from 923€

Return flights