Yes, it is the Northern Indiana Commuter Train District. Inside Chicago, they run on Metra track. To avoid competition with Metra, they do not allow boarding on "inbound" trains inside of Illinois (except the Hegewisch station that is on the Illinois/Indiana border), and do not allow people to get off "outbound" trains until the Hegewisch station [1]
Funny thing, is that Chicago has direct rail access from downtown to 4 airports in 3 states - Chicago O'Hare and Chicago Midway via the CTA, Milwaukee Mitchell (via Amtrak), and South Bend Regional (via the South Shore).
Funny thing, is that Chicago has direct rail access from downtown to 4 airports in 3 states - Chicago O'Hare and Chicago Midway via the CTA, Milwaukee Mitchell (via Amtrak), and South Bend Regional (via the South Shore).
[1] https://en.wikipedia.org/wiki/South_Shore_Line