Krajewski, from the city's Port Richmond section, retired last year after serving on council for 32 years.
She suffered from health problems in recent years.
In a statement issued Thursday morning, Council President Darrell Clarke said, "Joan was a great champion of Northeast Philadelphia. She was an unfailingly supportive colleague. And more importantly, she was my friend."
"I hope what Philadelphians remember most about Joan is she was a genuinely caring, warm, good human being. My heartfelt condolences go to Joan's sons and to all others who were privileged to know her," Clarke said.
Krajewski was 79 years old.