Holdridge was born Cheryl Lynn Phelps in New Orleans, Louisiana. Her mother, Julie A. Phelps (1908–2003), was a Dancer who performed on Broadway with her partner, Dick Mason; Cheryl's biological father is unidentified. Shortly after Cheryl was born, Julie moved with her new daughter to Burbank, California. In 1950, Julie married Herbert Charles Holdridge, a retired Brigadier General active in fringe political movements. He adopted Cheryl in 1953 and gave her his surname.
Her third husband, Manning J. Post (1918-2000), was active in Democratic politics in California. He died at the age of 82. All of her marriages were childless.
She auditioned for Walt Disney's The Mickey Mouse Club in the spring of 1956, and was hired for the club's "Red Team" — the most visible and popular of the Mouseketeers. Though a good Dancer, her weak singing voice kept her in the background of most musical numbers. A competent Actress with a pleasant speaking voice, she was employed for two of the show's episodic serials: Boys of the Western Sea and Annette.
In May 1960, Holdridge went on a live tour to Australia with other former Mouseketeers. While there, she became involved with Lucky Starr, an Australian singer. She was later linked in fan magazines and gossip columns with many other celebrities, including Elvis Presley.
After the show's run ended, Holdridge returned to Van Nuys High School and graduated from Grant High School with the winter 1961 class. She was cast in two episodes of Leave It to Beaver in 1959 as Gloria Cusick; she later played an occasional, recurring role as Wally Cleaver's girlfriend, Julie Foster.
Holdridge's first marriage was to sportsman and playboy Lance Reventlow, the only child of Woolworth heiress Barbara Hutton; his father was a Danish count. During their 1964 honeymoon in Hawaii, Holdridge became the last Mouseketeer to visit with the show's original host, Jimmie Dodd, before Dodd's death from cancer. Reventlow, a pilot, died in 1972, in the crash of a small plane in which he was a Passenger. She was styled as Gräfin von Haugwitz-Hardenberg-Reventlow.
After the death of her third husband, Holdridge made a cameo appearance in the 2000 feature film, The Flintstones in Viva Rock Vegas. In 2005, she appeared at Disneyland for 50th anniversary celebrations of both the opening of the park and The Mickey Mouse Club. She was cast in televised documentary specials about Cary Grant (2005) and Barbara Hutton (2006), and also appeared in a special feature interview for a Disney DVD.
Holdridge died on January 6, 2009 from lung cancer, aged 64.
