Found this WTTW video just put up as part of the Hidden Chicago 2 series that is coming Monday, November 30 at 7:30 pm. This particular video gives some very interesting history of Chicago's theater including the Oriental, the Congress, the south-side Regal Theater, the Uptown theater (built for $4 million in 1925 with 4,300 seats), and the Rialto. It also mentions many of the abandoned theaters throughout Chicago.
Apparently there were more then 350 theaters in Chicago by the mid 1920s.
Here's a link to the WTTW Hidden Chicago 2 website.