AirHint found the following cheapest return flights from Chicago (ORD) to Lisbon (LIS) in September 2025 (see full year).

Return flights

27 Sep - 05 Oct	Icelandair
24 Sep - 02 Oct	Icelandair
28 Sep - 08 Oct	Air Canada
22 Sep - 02 Oct	Aer Lingus
03 Sep - 11 Sep	KLM
23 Sep - 30 Sep	Aer Lingus
30 Sep - 07 Oct	SWISS
03 Sep - 12 Sep	KLM
29 Sep - 06 Oct	KLM
24 Sep - 01 Oct	Delta
21 Sep - 29 Sep	SWISS
16 Sep - 25 Sep	Delta
20 Sep - 24 Sep	Aer Lingus
25 Sep - 02 Oct	Air Canada
28 Sep - 05 Oct	Aer Lingus
05 Sep - 11 Sep	Frontier Airlines
24 Sep - 03 Oct	KLM
21 Sep - 25 Sep	Aer Lingus
16 Sep - 26 Sep	Air Canada
05 Sep - 11 Sep	TAP	direct

Also check the deals for one-way flights from Chicago to Lisbon 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 Lisbon in September from $543

Return flights