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

Return flights

29 Sep - 15 Oct	Turkish Airlines
15 Sep - 19 Oct	Turkish Airlines
08 Sep - 12 Oct	Turkish Airlines
28 Sep - 12 Oct	Turkish Airlines
21 Sep - 27 Oct	Spirit Airlines
29 Sep - 25 Oct	Frontier Airlines
25 Sep - 02 Oct	TAP
28 Sep - 30 Sep	Frontier Airlines
04 Sep - 26 Sep	Frontier Airlines
07 Sep - 18 Oct	SWISS
01 Sep - 16 Sep	SWISS
20 Sep - 02 Oct	Spirit Airlines
02 Sep - 09 Sep	United
01 Sep - 18 Sep	SWISS
01 Sep - 29 Sep	SWISS
14 Sep - 19 Oct	SWISS
03 Sep - 17 Sep	Lufthansa
02 Sep - 16 Sep	SWISS
04 Sep - 27 Sep	Frontier Airlines
12 Sep - 17 Sep	Frontier 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.

Book a cheap hotel in Sofia

Cheap car rent in Sofia

Cheapest return flights from Chicago to Sofia in September from $535

Return flights