Robert Feder, a media analyst from Chicago is reporting that the CW will be moving from WGN to WPWR.

From RobertFeder.com

In a rare change of network affiliations in Chicago, the CW Network will move this fall from Tribune Media WGN-Channel 9 to Fox-owned WPWR-Channel 50, sources said Sunday. The switch, expected to be announced Monday, will return “Chicago’s Very Own” to an independent station with a strictly local programming lineup, starting in September. Tribune Media still owns CW affiliates in 12 other markets, including New York and Los Angeles
Variety reports the story.
Twelve Tribune-owned stations will continue to broadcast the network, accounting for more than 28 million households, or more than 25% of the U.S.

The stations extending their affiliation agreements with The CW include WPIX-TV in New York, KTLA in Los Angeles, KDAF in Dallas, WDCW in Washington, DC, KIAH in Houston, WSFL-TV in Miami, KWGN-TV in Denver, KPLR-TV in St. Louis, KRCW-TV in Portland, WCCT-TV in Hartford, WGNT in Norfolk and WNOL-TV in New Orleans.
Deadline has more details.

We'll update as news comes in. No word as to when the switch will be made or how it will affect ratings.