"He will be missed but he will live on forever," the 61-year-old McCormick told ABC.
She called Cassidy a "really, really sweet person" who would make girls faint.
"They would go crazy," she recalled. "I had a huge crush on him, just as every person in America did."
McCormick said she wouldn't watch The Brady Bunch, but she would watch Cassidy on The Partridge Family. Both shows originally aired on ABC, with The Brady Bunch debuting in 1969 and Partridge a year later.
"That feathered perfect shiny hair. He could do it all….He just had that it factor," she said of Cassidy.
McCormick, who is only six years younger than Cassidy, previously spoke out about his death at the Los Angeles Mission Thanksgiving dinner last month.
“I wanted to be a member of that family on that bus with all that '70s love,” McCormick said. “I loved him so much. Such a good human, so much love.”
Cassidy died on Nov. 21 at age 67, following several days in the hospital. He died of liver failure, only months after publicly announcing he was diagnosed with dementia.
"I have known, loved, and admired David Cassidy for 48 out of my 58 years," Partridge Family co-star Danny Bonaduce tweeted after Cassidy's death. "He has been as kind to me as any real brother could ever be. We’ve been through a lot together and he was always there for me. This loss is huge. RIP my dear friend."