You are referring to the former Milwaukee Road Dunning Line which was cut back in stages to just north of Diversey. You can still see a slight hump in Irving Park Road where the tracks once crossed the street to enter the hospital grounds.
The tracks are in place but no longer in use from where they leave the mainline and up to Diversey. The Soo Line (later absorbed by parent company CP Rail)
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Forgotten Chicago Sightings