The ninth season of American Idol premiered on Fox on Tuesday, January 12, 2010, and concluded on Wednesday, May 26, 2010.^[1] Simon Cowell, Kara DioGuardi, and Randy Jackson returned as judges and were joined by Ellen DeGeneres, who was brought on as a replacement for Paula Abdul after a series of guest judges filled in during the auditions. Idol Gives Back also returned on April 21, 2010.^[2] The top 24 semifinal format used in the fourth through seventh seasons also returned this season.^[3] Cowell, DioGuardi, and DeGeneres all left the show after this season, although only Cowell's departure was announced in advance.^[4][5][6]

Lee DeWyze, a folk rocker from Mount Prospect, Illinois, won the competition, beating out fellow folk rocker Crystal Bowersox, who was the runner-up. Multiple contestants from this season were signed to record deals, including DeWyze, Bowersox, Casey James, Michael Lynche, and Siobhan Magnus.

Paula Abdul did not return to the judges panel, having announced in the beginning of August 2009 that she was leaving the show due to unresolved contract negotiations.^[7] Victoria Beckham, Mary J. Blige, Shania Twain, Katy Perry, Avril Lavigne, Joe Jonas, Neil Patrick Harris, and Kristin Chenoweth were brought on as guest judges during the auditions.^{[8][9][10][11]}

After making the decision to utilize guest judges in Abdul's absence, Fox chairman Peter Rice stated that they would find a permanent fourth judge before the season premiere in January 2010.^[12] Ellen DeGeneres confirmed on September 9, 2009, that she would be joining the show as the new permanent fourth judge for the rounds held at CBS Television City for Hollywood Week and thereafter.^[13]

Additionally, Simon Cowell announced shortly before the ninth season began that it would be his last season on American Idol. Cowell left the show to begin preparations for an American version of his singing competition The X Factor.^[14] Ellen DeGeneres also announced on July 29, 2010, that she would not return to the judges panel because it was not the "right fit" for her.^[15] Kara DioGuardi also announced on September 3, 2010, that she would not return as a judge for the tenth season.^[16]

Auditions began on June 14, 2009, less than a month after the previous season's finale. During this stage, a series of guest judges filled in on the judging panel.^[17] Auditions were held in the following cities.^[18]

Held at the Kodak Theatre for the second straight year, the first day of Hollywood Week featured the 181 contestants from the auditions round^[27] singing solo with the option of playing an instrument.^[28] Ellen DeGeneres made her first appearance as a judge at this time. 96 contestants advanced. The next round required the contestants to split into groups and perform. 71 advanced to the final round of Hollywood requiring a solo performance. 46 made it to the final round, where the judges spoke to the contestants one-by-one to tell them whether they had made the final 24.^[29]

The semifinal format used during the fourth through seventh seasons was revived for this season. Starting with twelve women and twelve men, the women and men performed weekly on separate shows, each performing a Billboard Hot 100 song, and on the results show, the bottom two contestants from each group were eliminated from the competition. The semifinals took place over three weeks, meaning that six men and six women were eliminated, leaving the other six men and six women to form the top 12. The women performed on the first night, and the males the next night. However, the men and women switched on March 2 and March 3, because Crystal Bowersox had been hospitalized due to complications from diabetes.^[30][31]

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• Lee DeWyze (born April 2, 1986, in Mount Prospect, Illinois; 23 years old at the start of the show) was from Mount Prospect, and auditioned in Chicago with Bill Withers' "Ain't No Sunshine." He performed The Fray's "You Found Me" in Hollywood.
• Crystal Bowersox (born August 4, 1985, in Elliston, Ohio; 24 years old at the start of the show) was from Elliston, and auditioned in Chicago with Erma Franklin's "Piece of My Heart." Her Hollywood performance of Aretha Franklin's "(You Make Me Feel Like) A Natural Woman" impressed the judges and fellow contestants alike. She was diagnosed with Type 1 diabetes when she was six, and while on the show, she suffered diabetic complications and was hospitalized, which resulted in the top 20 performance nights for the male and female contestants to switched.
• Casey James (born May 31, 1982, in Princeton, Texas; 27 years old at the start of the show) was from Fort Worth, Texas, and auditioned in Denver with John Mayer's "Slow Dancing in a Burning Room."
• Michael Lynche (born May 31, 1983; 26 years old at the start of the show) was from St. Petersburg, Florida, and auditioned in Orlando with Todd Duncan's "Unchained Melody." His daughter was born during the Hollywood round, and the unfolding drama of his wife's labor was heavily featured while he performed John Mayer's "Waiting on the World to Change."
• Aaron Kelly (born April 2, 1993, in Davenport, Florida; 16 years old at the start of the show) was from Sonestown, Pennsylvania, and auditioned in Orlando with Miley Cyrus's "The Climb." He performed Sarah McLachlan's "Angel" in Hollywood, where he forgot his words.
• Siobhan Magnus (born March 15, 1990, in Barnstable, Massachusetts; 19 years old at the start of the show) was from Cape Cod, Massachusetts,^[32] and auditioned in Boston with Queen's "Love of My Life." She performed Stevie Wonder's "Living for the City" in Hollywood.
• Tim Urban (born May 1, 1989, in Tacoma, Washington; 20 years old at the start of the show) was from Duncanville, Texas, and auditioned in Dallas with Matt Nathanson's "Bulletproof Week." He performed David Cook's "Come Back To Me" in Hollywood. He did not initially qualify for the semifinals, but was chosen as a replacement when Chris Golightly was disqualified from the competition.
• Katie Stevens (born December 8, 1992, in Southbury, Connecticut; 17 years old at the start of the show) was from Middlebury, Connecticut, and auditioned in Boston with Glenn Miller's "At Last." She performed Jean DuShon's "For Once in My Life" in Hollywood, where Kara DioGuardi considered her a potential winner.
• Andrew Garcia (born October 8, 1985, in Moreno Valley, California; 24 years old at the start of the show) auditioned in Los Angeles with Maroon 5's "Sunday Morning." He impressed the judges with his performance of Paula Abdul's "Straight Up" in Hollywood.
• Didi Benami (born October 25, 1986, in New York City, New York; 23 years old at the start of the show) was from Knoxville, Tennessee, and auditioned in Los Angeles with The Beatles' "Hey Jude." She performed Katharine McPhee's "Terrified" – penned by Kara DioGuardi – in Hollywood.
• Paige Miles (born September 26, 1985; 24 years old at the start of the show) was from Naples, Florida, and auditioned in Dallas. She performed Stevie Wonder's "Living for the City" in Hollywood.
• Lacey Brown (born August 13, 1985; 24 years old at the start of the show) was from Amarillo, Texas, and auditioned in Orlando with Judy Garland's "Over the Rainbow." She had previously made it to the Hollywood round in the eighth season of American Idol. Ryan Seacrest noted that her performance of "What a Wonderful World" by Louie Armstrong had a major part in her advancing into the top 24.

There were eleven weeks of finals with twelve contestants competing. At least one contestant was eliminated every week based on the public's votes, although the judges could veto one elimination through the use of the "judges' save."

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Chris Golightly was originally selected as semi-finalist. According to reports, Golightly was disqualified on February 17, 2010, after already being told he was in the top 24, over an old contract. The contract had expired by the time the top 24 began to tape, but they disqualified him because he was under contract at the time of the tryouts, in violation of Idol rules. He was later replaced by Tim Urban at the last minute of the last part of Hollywood Week.^[33]

Ryan Seacrest was criticized by TheWrap and MSNBC Entertainment for "critiquing the judges’ comments" and becoming more aggressive.^[34][35] Ratings for this season dropped significantly compared to the previous two seasons,^[36] leading to speculation that it might be coming to a close.^[37] It was speculated that reasons for the decline might have included the pending departure of Simon Cowell and the more unpredictable behavior of Ryan Seacrest.^[38]

This season of American Idol was the top show for the 2009–10 season of broadcast primetime shows. Its Tuesday and Wednesday episodes occupied the top two spots of the season. Viewership for the Tuesday episodes averaged 22.974 million, while the Wednesday episodes averaged 21.951 million.^[39]

• American Idols LIVE! Tour 2010