The voice-over actress died at the age of 96 after a long brain tumour condition considered inoperable according to reports.
The news of her death was confirmed by her daughter, who told ABC News.
Waldo was a voice character in cartoon series such as The Perils of Penlope Pitstop and The Flinstones.
She died on Sunday, June 12, 2016, after been diagnosed with a brain tumour condition that has lasted for five years.
Her most recent role was in 1998, where she played Mrs Tobbis, in the animated TV series, King of the Hill.
Before her passing, Waldo was credited for her appearance in 100 TV and movie series.