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

Return flights

27 Sep - 20 Oct	Air France
22 Sep - 18 Oct	Air France
18 Sep - 25 Sep	United
27 Sep - 30 Sep	Spirit Airlines
28 Sep - 10 Oct	Spirit Airlines
27 Sep - 02 Oct	Icelandair
20 Sep - 25 Sep	Aer Lingus
22 Sep - 26 Sep	Spirit Airlines
21 Sep - 26 Sep	Frontier Airlines
19 Sep - 24 Sep	Aer Lingus
20 Sep - 11 Oct	Frontier Airlines
19 Sep - 26 Sep	Frontier Airlines
26 Sep - 26 Oct	SWISS
16 Sep - 11 Oct	Frontier Airlines
19 Sep - 27 Sep	Frontier Airlines
18 Sep - 25 Sep	TAP	direct
20 Sep - 11 Oct	TAP	direct
16 Sep - 26 Sep	United
27 Sep - 05 Oct	TAP	direct
27 Sep - 02 Oct	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 562€

Return flights