The man was taken into police custody and charged, but the investigation into how exactly he was able to board the aircraft continues.
Tuesday night, Chicago resident Elvis Jackson, 33, boarded Southwest Airlines Flight 908 headed from Chicago to Birmingham, Ala. Other passengers noticed the man snuck past the gate and alerted officials.
Police escorted the man off of the plane. The flight was cleared for takeoff approximately one hour later.
Jackson faces two counts of misdemeanor trespassing and was being held at Chicago Police District 8 Wednesday morning.
It is unclear whether Jackson was already in Midway's gated terminal area after a previous flight or if he got through TSA security without a boarding pass.
Passengers at Midway Wednesday morning expressed concern about the issue.
"A little scared, a little scared. It inconveniences people and they complain about it, but I think we all should be inconvenienced for our safety," traveler Adrienne Svetich said Wednesday.
"There are so many checkpoints here, how could somebody get through all of them without a boarding pass?" traveler Suzanne Mallo said.
Some answers could come later Wednesday after the suspect's appearance in court.