From Porter it looped to the southwest and northwest, joining the Illinois Central Railroad in the Kensington neighborhood of Chicago.

Eventually the NYC started to operate most trains west from Porter via the LS&MS, and the MC became a secondary route.

With the 1998 breakup of Conrail, CSX Transportation acquired the branch, by then only running from Porter west to Gibson, located in Hammond, Indiana, a junction with the east-west Indiana Harbor Belt Railroad and the north-south Kankakee Line, transferred from Conrail to the Norfolk Southern Railway.

To the east, a connection existed at Tolleston to the Fort Wayne Secondary, also acquired in the 1998 Conrail breakup (though from the Norfolk Southern Railway).

CSX has considered putting in diamonds, but has held off for now (they use NS west of Porter to reach their Grand Rapids Subdivision).