Trains from Indianapolis to O'Hare Airport?
There's one train each day, operated by Amtrak, that goes from Indianapolis to downtown Chicago. From there, you can use the Chicago transit system (CTA), to get to the airport.
All Amtrak trains serving Chicago arrive at Union Station. The best way to travel from Union Station to O'Hare airport is by the CTA rail.
Unless there is something I don't know about here, there are no trains to O'Hare Airport. At one time there was a train from Indianapolis to Chicago but not sure if it runs any more.
check the city bus route website