First off, the post title is not a typo, I know that the Chicago Railroad Fair ran for two seasons, 1948 and 1949!
That said, it seems that C&S No. 9 and its train remained in Chicago for the summer of 1950, as seen on the postcard below;
This seems to be a pretty standard postcard of No. 9 and train from the Fair. Though not as common as the color card issued by the CB&Q, this card (made by a company in Chicago) is not super hard to find.
What makes this one interesting is the postmark:
Notice the date - August 19, 1950. Also note the station (ie post office) on the postmark - "CHICAGO FAIR STATION". (from what I can find, this is the official post office that the USPS set up at the Fair grounds)
As it turns out, this card was issued in 1950 for the "1950 Chicago Fair", an entirely new and different event held on the grounds of the 1948-49 Chicago Railroad Fair. The 1950 Chicago Fair ran from June 24 to September 4, 1950 and this card is one of series of 10 cards from the fair.
As the card shows, No. 9 and its train were on hand to run around the fairgrounds for a third summer.
Jason Midyette