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

Return flights

01 Sep - 18 Sep	SWISS
01 Sep - 16 Sep	SWISS
02 Sep - 16 Sep	Lufthansa
10 Sep - 17 Sep	Lufthansa
24 Sep - 01 Oct	United
30 Sep - 07 Oct	United
29 Sep - 13 Oct	Lufthansa
09 Sep - 16 Sep	United
03 Sep - 10 Sep	United
21 Sep - 29 Sep	Lufthansa
15 Sep - 22 Sep	United
04 Sep - 26 Sep	Lufthansa
18 Sep - 25 Sep	United
27 Sep - 04 Oct	United
19 Sep - 06 Oct	Spirit Airlines
23 Sep - 07 Oct	Turkish Airlines

Also check the deals for one-way flights from Chicago to Sofia 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 Sofia in September from 464€

Return flights