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

Return flights

23 Sep - 16 Oct	Virgin Atlantic
22 Sep - 15 Oct	KLM
22 Sep - 16 Oct	KLM
09 Sep - 16 Sep	Delta
08 Sep - 17 Sep	Delta
09 Sep - 19 Sep	Delta
06 Sep - 18 Sep	Virgin Atlantic
21 Sep - 30 Sep	Delta
12 Sep - 17 Sep	KLM
26 Sep - 01 Oct	Air France
04 Sep - 10 Sep	Delta
11 Sep - 14 Oct	Delta
07 Sep - 22 Sep	Delta
28 Sep - 05 Oct	Delta
09 Sep - 05 Oct	Delta
03 Sep - 20 Sep	Air France
07 Sep - 21 Sep	KLM
15 Sep - 21 Oct	Virgin Atlantic
14 Sep - 21 Oct	Virgin Atlantic
22 Sep - 14 Oct	Air France

Also check the deals for one-way flights from Chicago to London 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 London in September from 435€

Return flights