Blackwell's son Jeremiah Blackwell Jr. confirmed the news to the Mississippi Today, adding that his mother had a long battle with the disease.
Blackwell, known widely for her activism and role in desegregation during the Civil Rights Movement, was born in Lula, Mississippi, in 1933.
As a child, she fled her home state for West Helena, Arkansas, where Black students were allowed to attend school. After marrying Jeremiah Blackwell, and moving to Florida, Blackwell worked "odd jobs," such as at a canning factory during harvest seasons.
In 1962, Blackwell relocated to Mississippi as the Civil Rights Movement began to pick up steam.
Along with volunteering in voter registration efforts, she worked as a director for the Student Nonviolent Coordinating Committee (SNCC) and was arrested more than 70 times during the fight for Black voting rights and voting registration.
"I was put into the position of learning to survive, someway and somehow, by being black and in this country," Blackwell said in a 1977 oral history interview with the University of Southern Mississippi obtained by Mississippi Today. "But also being black and in this country, you learn a great lesson, and this is how to overcome. … It’s that power to move in the midst of opposition."
Her work in the field garnered the attention of the federal government and she was brought on as an adviser for presidents Lyndon B. Johnson, Richard Nixon, Gerald Ford, Jimmy Carter, Ronald Reagan and Bill Clinton.
She made history in 1976 by becoming the first Black woman to be mayor of Mayersville, Mississippi, where she served five terms. Blackwell was awarded the prestigious MacArthur Foundation’s Genius Grant in 1992.
Congressman Bennie Thompson, (D-Ms.), said, "I am saddened by the passing of Unita Blackwell. She dedicated her life to fighting for civil rights in Mississippi. We are forever grateful for her work and sacrifice. My thoughts and prayers are with her family and all those who loved her."