If you had already planned on being in the Chicago area the weekend of the 25th and 26th,
allow me to highly recommend a visit to the following -
Illinois Railway Museum - Union IL
Steam is not listed, but call the Museum to check what equipment will be running. The museum is among the largest in the nation and diesel and electric trains operate every weekend, as well as trolley cars.
Greenfield Village - Dearborn MI
A little drive from Chicago area, but totally worth it. Steam Locomotive operates daily at the Henry Ford Museum Greenfield Village. A working roundhouse, coal tower, and water tower can be seen in the village, and next door the Henry Ford Museum features various locomotives including an a beautiful 4-4-0 built in 1860, and the massive Allegheny articulated locomotive.
Little River Railroad - Coldwater MI
Not too far from the Greenfield Village (hint hint!) The Little River Railroad is operating Sunday June 26th. Locomotive #110, a lovely coal burning 4-6-2 steam locomotive, will be pulling 45 minute excursion.
Hesston Steam Museum - Hesston IN
A short drive from Chicago, the Hesston Steam Museum operates 4 gauges (36", 24", 14" and 7.5") of equipment on 3 separate railroad routes. The weekend of the 25th is the Civil War Weekend, and steam will be operating on each railroad. Shay #7, a wood burning 36" gauge Shay, is always a treat to see in operation.