Commuter trains connecting the suburbs around Chicago are available and may in some cases be usefull to you when moving around the area. Some students and postdocs who live in the city of Chicago take the METRA/UNION Pacific West Line from the O'Gilvie Transportation Center at Chicago to the Geneva Metra Station, or the METRA/BNSF Railway from Union Station at Chicago to the Route 59 station in Naperville as part of their daily commute. However it is necessary to have a car to go from the train stations to Fermilab. At present the lab does not provide a taxi service to or from train stations.
A typical commute from downtown using one of these two lines should last approximately between 50-60 min on the train plus 15-25 min drive from the station to the lab. If you do not live nearby Union Station in Chicago, you should consider the extra time it will take you to get there from your home.
For more information on transportation by train see section 8.1.2 of this guide.