The main suburban routes in the Chicago area have never lost their passenger services, control and financing of them just moved from the owning railroads to the Regional Transportation Authority in the mid-1970s, with the railroads continuing to operate the services under contract (this is still the case with the services on BNSF & UP tracks, the other routes are now directly operated by Metra staff).
If you haven't been to Chicago before, if the weather is decent take a ride out to somewhere like Hinsdale (on the BNSF line) in the late weekday afternoon and watch the trains go by - peak Metra service (all loco hauled push-pull) intermingled with freight and Amtrak trains on a busy triple-track line. La Grange station (same route) is also good, with the bonus of the IHB freight route within walking distance (the line passes under the BNSF line just east of the station).
But passenger service on some Metra Rail lines is limited, such as the Heritage Corridor route to Joliet via Lockport, and the South West Service to Manhattan (Illinois) which only operate at peak hours and have no weekend service.
The Rock Island Line to Joliet via Blue Island - Vermont has a regular service all day, seven days per week.
I have been to Chicago before.
I would recommend a trip on the South Shore line, which is one of the last interurban railroads still running in the United States.
At Michigan City, Indiana, you have full size trains running in the middle of the street as if they were a tram, and the "stations" at 11th Street and Carrol Avenue
were little more than a bus stop with a shelter. It is quite a surprise to hear the train horn blasting in the distance, and a full size train coming round the corner.
shows a Chicago bound train arriving at the old 11th Street station in Michigan City.
However 11th Street station has now been closed for reconstruction and installation of high level platforms.
Trains are also going to be separated from other traffic, similar to a tramway reservation.
PS.
I presume you know that
Railfanning is the U.S. term for
Trainspotting.