Tormented to the last after a lifetime of campaigning, the 78-year-old died without fulfilling her cherished wish to find her son's makeshift grave on Saddleworth Moor and give him a proper Christian burial.
Glasgow-born Ian Brady and Myra Hindley abducted and murdered the 12-year-old in 1964, the only one of the five young victims whose body has never been found.
At the service at St Chrysostom's Church, in Victoria Park, Manchester, where Mrs Johnson, a widow, was a regular parishioner and Keith attended Sunday school, the names of her son's killers were never uttered once.
Instead her family, friends and ordinary members of the public among the mourners heard tributes to a courageous mother who battled on despite a life touched by tragedy.
Canon Ian Gomersall, rector of St Chrysostom's, told mourners she lived all her life in Manchester, where her son was abducted. "I will not go into the detail of this, nor will I name here the perpetrators of that evil," he said.
"What I will do is pay tribute to this remarkable woman. I know my words of tribute will be shared by so many people."
Canon Gomersall said Mrs Johnson had shown "that we, everyday people, can have courage, strength, hope and determination, whatever assails us".
Grandson Stephen Prescott said his grandmother was the centre of the family.
Before the service began, the coffin arrived in the hearse surrounded by floral tributes, one incorporating a photo of Mrs Johnson.
Other floral tributes spelled out "Gran" and "Mam" and there were wreaths from her local Gala Bingo club, one of Mrs Johnson's favourite pastimes, and another from Greater Manchester Police.