(CNN) Civil rights activist Unita Blackwell made history in 1976, becoming Mississippi's first black female mayor. She died on Monday at age 86.

Unita Blackwell may have been born into humble beginnings on March 18, 1933, but her activism and courage helped change the course of history for African-Americans.

Her son, Jeremiah Blackwell Jr., told CNN his mother died from a buildup of fluid in her heart and lungs, after a lengthy battle with dementia and Alzheimer's disease.

Blackwell was the first black female mayor in Mississippi, elected as mayor of Mayersville 12 years after the passage of the Civil Rights Act of 1964.

Unita Blackwell, shown in 1992, long advocated for voting and other rights.

As an active member in the Student Nonviolent Coordinating Committee (SNCC), Blackwell helped African-Americans register to vote.

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