When Unita Blackwell became mayor of Mayersville, Miss., many of the town’s roughly 500 residents lived in tin-roof shanties with no running water. There was no sewer system, and the streets were unpaved. The year was 1976, but the town carried on much as it had for generations, unnoticed by the world beyond the Mississippi Delta.

For her efforts to modernize and improve the living conditions in her town, Mrs. Blackwell — a former civil rights worker whose early education ended at eighth grade, and who had once chopped cotton for $3 a day — received a MacArthur Foundation grant in 1992 worth $350,000. The award, commonly called a “genius” grant, brought national attention to Mrs. Blackwell, to Mayersville and to the struggles of rural communities like it.

Mrs. Blackwell, who was reportedly the first black woman to serve as a mayor in Mississippi, spending two decades leading her town from the one-room city hall that had formerly been a Baptist church, died May 13 at a hospital in Ocean Springs, Miss. She was 86. The cause was a heart and lung ailment, said her son, Jeremiah Blackwell Jr.

A daughter of sharecroppers, Mrs. Blackwell joined the civil rights movement in the 1960s. Recruited to the Student Non-Vio­lent Coordinating Committee, she was arrested more than 70 times, by her count, for her efforts to register African American voters. The Ku Klux Klan burned crosses in her yard. Molotov cocktails exploded outside her home.

Even after the Civil Rights Act of 1964 and the Voting Rights Act of 1965, which outlawed discrimination in employment, public accommodations, the voting booth and elsewhere, deep economic inequality persisted, leaving Mayersville and other largely black communities mired in poverty. It was this inequality that Mayor Blackwell sought to rectify, if only in­crementally, as she defended her hamlet’s way of life.

“People in urban areas seem to think . . . we’re backwards,” Mrs. Blackwell told The Washington Post in 1978. “We don’t have all the push-buttons, but anyone who lives with the land and is moved by the vibrations of the air has a real feeling for life.”

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Mrs. Blackwell, whose civil rights activism had led to work with the National Council of Negro Women and the Ford Foundation, first set about the task of incorporating Mayersville in the 1970s. “You can’t get federal dollars for housing if you’re not an incorporated town,” she told the Atlanta Journal-Constitution years later.

As the town’s first mayor, she spearheaded the establishment of public water and sewer systems. She oversaw the paving and naming of roads. Under her leadership, the town obtained its first firetruck.

Mrs. Blackwell stepped down as mayor to run, unsuccessfully, for the Democratic nomination for a U.S. congressional seat in 1993. She won election to another four-year term as mayor in 1997. By that time, there were “no shacks in Mayersville, only modest ranch homes built with Farmers Home Administration loans and several public housing projects,” the Atlanta newspaper reported.

Those housing projects included a $550,000 federally funded complex of 20 units for the elderly and disabled that opened in 1987. For some residents, it was their first home with indoor plumbing.

“Unita Blackwell has a way about her of getting things that can’t be gotten,” James Roland, a regional administrator for the U.S. Department of Housing and Urban Development, told The Post at the time.

“We were supposed to be enemies,” said Roland, who, according to The Post, displayed on his desk a bust of Confederate Gen. Robert E. Lee, “because I am a white Republican and she is a black Democrat, but the truth is that we got along very good.”

Unita Zelma Brown was born on March 18, 1933, in the Delta town of Lula, Miss., where she grew up on a plantation. Her father was forced to flee the state to avoid being lynched after he confronted a white man who had ordered Mrs. Blackwell and her mother into the field.

Mrs. Blackwell picked cotton with her mother when not living with relatives in Arkansas, where her mother had sent her for better schooling. She said her mother could not read or write but “was determined I would.”

She moved to Mayersville with her first husband, Jeremiah Blackwell Sr. That marriage ended in divorce, as did a subsequent one to Willie Wright. Besides her son, of Biloxi, Miss., survivors include four grandchildren and eight great-grandchildren.

Mrs. Blackwell said the “great turning point” in her life came in 1964, when she attempted to register to vote and was turned away. While participating in the Freedom Summer voter registration drive that year, she joined the Mississippi Freedom Democratic Party in an unsuccessful challenge to the all-white Mississippi delegation to the 1964 Democratic National Convention in Atlantic City.

All of her civil rights work, she said, grew from her desire to obtain a quality education for her son, whose schools she helped integrate.

“Most people who helped break down the walls were just moving a brick,” she told the New York Times, “because the brick was right in their face. For me, what was in my face was getting some books to my child, and giving him a chance to read and write.”

In 1973, actress Shirley Mac­Laine invited Mrs. Blackwell to join what was billed as a representative delegation of American women on a visit to China. The trip, which yielded MacLaine and Claudia Weill’s 1975 documentary “The Other Half of the Sky: A China Memoir,” was the first of many trips by Mrs. Blackwell to the Communist nation with a cultural-exchange organization.

“I came back with hope for America,” she said, “having seen another oppressed situation.”

Mrs. Blackwell served on a national council on women during President Jimmy Carter’s administration and twice led the National Conference of Black Mayors. In 1983, with only a high school equivalency diploma, she received a master’s degree in regional planning from the University of Massachusetts at Amherst.

In 2001, Mrs. Blackwell was defeated for reelection in a four-way race, having come in second with 71 votes, according to the Associated Press.

Mrs. Blackwell was the author of a memoir, “Barefootin’: Life Lessons From the Road to Freedom” (2006), written with JoAnne Prichard Morris. She was often asked why she remained in Mayersville, when she might have found an easier life elsewhere. She stayed because “this is my home,” she told The Post, and “because we had so much to do.”