Clooney died shortly after 6 p.m. due to complications from lung cancer, her publicist said. Her passing came just days after news surfaced that Clooney had suffered a relapse in her battle with the disease.
The entertainer's family--including her husband, dancer Dante Di Paolo, actor Miguel Ferrer (her son with first husband Josť Ferrer) and her brother, Nick (George Clooney's father)--had reportedly been by her side.
She initially underwent cancer surgery at the Mayo Clinic in Minnesota in January to remove the upper lobe of her left lung. A series of infections delayed her recovery, and she remained hospitalized until May.
She was finally given the okay to return home after doctors deemed her fit enough to resume singing and performing. But Clooney, a longtime smoker, checked back into the hospital after relapsing earlier this month.
As one of the last of the noted "Girl Singers," Clooney rose to fame in the 1950s alongside Ella Fitzgerald, Peggy Lee, Dinah Washington and Doris Day. She scored a string of hit singles including the mega-hit "Come On-a My House" (penned by Armenian-American writer William Saroyan), "Hey There," "This Ole House" and "If Teardrops Were Pennies."
Clooney then moved on to film and television, first with Paramount musicals such as The Stars Are Singing, Here Come the Girls with Bob Hope and White Christmas, with Crosby and Danny Kaye. On the small screen, she earned an Emmy nomination for her own TV series, the Rosemary Clooney Show, which ran from 1956 through 1957.
Her career, however, was derailed in the late 1960s due to personal trouble with drugs and alcohol. But by the '80s, she had successfully returned to the stage and in 1994, she earned her second Emmy nomination for a recurring role as an Alzheimer's patient on nephew George's ER.
Clooney was born in Maysville, Kentucky, in 1928, but was forced to grow up quickly, as her parents separated and she spent much of her childhood with other relatives.
She started her career with her younger sister Betty. By 1947, The Clooney Sisters were touring with Tony Pastor's big band. But when Betty decided to move back to Kentucky, Rosemary continued on to New York, and at age 21, signed with Columbia Records. 1951's "Come On-a My House" was her first big smash, selling more than a million copies. Hollywood musicals quickly followed.
Then in 1953, Clooney married Oscar-winning actor Josť Ferrer, and motherhood took precedence over her career. The pair had five children together before they divorced in 1961. The couple reconciled for three years, only to split for good in 1967.
Personal problems sent Clooney into a deep depression that led her to abuse painkillers and overeat. "My brink of despair was rushing up to meet me like the end of a runway for a plane lumbering in vain to get off the ground," she wrote in her autobiography, which later became a 1982 TV movie, Rosie: The Rosemary Clooney Story, starring Sandra Locke.
After years of therapy, Clooney eventually rebounded, joining Bing Crosby for a series of shows in Los Angeles, Chicago, New York and London in the 1970s.
Earlier this year, Clooney received a special lifetime Grammy award for her career achievements.
"Rosemary was a beloved friend to everyone who knew her," said songwriter Michael Feinstein, who worked with Clooney three years ago in New York. "She was a singer who made an incalculable contribution to American popular song by her extraordinary and wise interpretations of these classics."
Clooney is survived by her five children (Miguel, Maria, Gabriel, Monsita and Rafael), her husband, Dante Di Paolo, and her 10 grandchildren.