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

Return flights

01 Sep - 16 Sep	Turkish Airlines
01 Sep - 18 Sep	Turkish Airlines
21 Sep - 27 Oct	Air Canada
01 Sep - 08 Sep	Lufthansa
21 Sep - 29 Sep	Lufthansa
01 Sep - 29 Sep	Turkish Airlines
02 Sep - 09 Sep	United
10 Sep - 17 Sep	United
04 Sep - 08 Sep	Austrian Airlines
04 Sep - 09 Sep	Lufthansa
04 Sep - 11 Sep	United
25 Sep - 02 Oct	United
28 Sep - 05 Oct	United

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 $538

Return flights