Witnesses said she had just been dropped off at the station on Prospect Avenue, shortly after 8 a.m., when she was struck by train No. 1242., an express train that originated in Aurora and was scheduled to arrive in Chicago at 8:15 a.m.
Video from nearby security cameras shows her crossing the tracks as the gates were down, police said.
"I've seen a lot of people cross the tracks, both there and on the - there's another area, over there, where they can cross. There is usually a police officer that is here for the last express train. The 8:54 is more of a local train. But after 8:54, you have to wait an hour for the next one. So there is a sense of urgency, in terms of trying to catch that, so you don't have to wait an hour for the next one," said Eyleen Hawkins, a Metra commuter.
Metra police later said the woman had died. She lived in west suburban Oak Brook. Her identity has not yet been released.
"We ask that everyone keep the family of the deceased in their thoughts and keep in mind the importance of pedestrian safety at rail crossings," police said.
BNSF service was stopped in both directions until around 10:45 a.m. Extensive delays were expected.
Officials asked commuters to listen to platform announcements and check out Track Your Train on metrail.com for real-time updates.
The Sun-Times Media Wire contributed to this report.