(Recasts with ratings figures and background on programming)
LOS ANGELES, May 29 (Reuters) - Kevin Reilly, the top executive at Fox broadcast television, is leaving the network next month, the company said on Thursday, after Fox slumped to last place in ratings among the big U.S. broadcasters.
Reilly's seven years as chairman of entertainment at Twenty-First Century Fox Inc's broadcast division ended with marquee programs like "American Idol" and "Glee" suffering sharp ratings drops.
Fox has also lost its top ranking among viewers in the 18-49 age group that advertisers value most.
Reilly said in a statement that he and Fox Networks Group chairman and chief executive officer, Peter Rice, had been discussing his departure for a while.
"It felt like the timing was as right as it could be," Reilly, who joined Fox in 2007 and was named chairman of entertainment in 2012, said in the statement.
The move comes after the network presented its fall stable of programming to advertisers earlier this month.
Fox said that Reilly's senior executives will report to Rice before the company names a replacement.
The network averaged 7.3 million in daily primetime viewers this past season, according to Nielsen data. That was up from 7 million last year, but Fox fell one place to fourth behind, CBS, NBC and ABC, respectively.
Its record haul of 111.5 million viewers in February for football's Super Bowl did not deliver a significant improvement on overall viewership.
The Super Bowl also failed to boost the coveted 18-49 audience, which remained flat and in second place with 3.1 million viewers on average.
Fox's current entertainment slate consists of critically acclaimed shows such as "The Mindy Project," "Brooklyn Nine-Nine" and "New Girl," but the shows have so far been unable to become ratings powerhouses for the network.
In addition to struggling with falling audiences for "American Idol" and "Glee," the network jettisoned Simon Cowell's singing contest "The X Factor" in February after three seasons.
Fox also canceled the anticipated science-fiction drama "Almost Human" from executive producer and "Star Trek" director J.J. Abrams after one season.
Fox was the top draw in the 18-49 age group for eight consecutive years before it was knocked to second in the 2012-13 season.
NBC, under the ownership of Comcast Corp has managed to make a big comeback and now is the top network in the 18-49 age group.
Reilly joined Fox from NBC, where he was the president of entertainment and oversaw the development of shows like hit comedies "The Office" and "30 Rock."
Reilly is also credited with helping usher in the current era of acclaimed and well-rated cable television from his time at Fox's cable network FX where he introduced drama series such as "Nip/Tuck" and "The Shield."
(Editing by Mary Milliken and Tom Brown)