Where did the Erie track end as it approached Chicago? What route did the passenger trains take into the city? Did the CHicago & Atlantic and Erie use the same depot through the years?
Erie used the Chicago and Western Indiana track to get into Chicago. The change from Erie RR tracks occurred around the Indiana / Illinois border.
Erie passenger trains terminated at Dearborn Station on Polk Street. The station still stands, but the train shed and tracks are long-gone. The station is currently used as a sort of mall, with shops and offices.
I'm not familiar with the Chicago and Atlantic.
JR