Hotel is 2 blocks south of the Blue Line Rosemont CTA station that goes into downtown Chicago (Chicago Loop).
The train station is about 1/2 mile from the Doubletree hotel.
The train station is about 1/2 mile (15 min.)walk from Doubletree at Rosemont.
My transportation was by their shuttle from and to O'Hare. The train is just inside the drop off point. The shuttle runs frequently and is free.
While I did not access the public transportation, I was told it was only a few min away and very easy to use. 35-40 min ride for only a few bucks. ;)
Get an answer from Doubletree by Hilton Chicago O'Hare Airport - Rosemont staff and past guests.