She was taken to Lutheran General Hospital in serious-to-stable condition, the Chicago Fire Department said.
The woman was struck Tuesday around 2:30 p.m. outside the United Airlines Terminal 1 at O'Hare. She was in the outer lanes on the terminal's lower level.
The bus driver was cited. Jaime Flores, 50, of the 1500 block of North 43rd Street in Stone Park, was issued one citation for striking a pedestrian in a roadway, police said.
The Sun-Times Media Wire contributed to this report.