The mirror of a Megabus.com bus making a left turn on to Adams struck the Donna Halstead, 76, while she was walking north in crosswalk.
It happened around 2:15 p.m. There were no passengers on board the bus.
As paramedics arrived, witnesses say, Halstead was unresponsive. She was transported as a trauma patient to Northwestern Memorial Hospital in critical condition. A statement sent by Megabus.com later in the day indicated that Halstead had died.
"We are saddened to report this tragic incident," said Dale Moser, president and COO of megabus.com, in a statement. "Our thoughts and prayers are with everyone involved, particularly the family of the deceased woman."
The female bus driver remained on board for some time, speaking to investigators before leaving with police. She was cited with failing to yield to a pedestrian.
Police say the driver was taken to the hospital for blood and urine testing.
Halstead lives in a building at the same corner where the incident happened. Those who know her say she often crossed this intersection to bring lunch to her son, who works at Union Station.
The incident comes just five days after a double-decker Megabus was involved in a fatal crash near downstate Litchfield, Illinois.
In a statement, Megabus.com said all its arrivals and departures will continue to operate as scheduled. It also said it was cooperating with authorities to investigate the incident.