Family spokeswoman Elizabeth Christian said Mrs. Johnson died surrounded by family and friends. Mrs. Johnson, who had a stroke in 2002 that affected her ability to speak, had been hospitalized in June for a low-grade fever.
Mrs. Johnson, the widow of President Lyndon Baines Johnson, was "one of the kindest and most caring and compassionate people I've ever met in politics," Sen. Edward M. Kennedy (D., Mass.) said in a statement. Former first lady Nancy Reagan said Mrs. Johnson served the nation with honor and dignity.
Mrs. Johnson will lie in repose at the LBJ Library and Museum from 1:15 p.m. Friday until 11 a.m. Saturday. A private funeral will be held Saturday afternoon, and a ceremonial cortege will carry her body to Stonewall for burial in the Johnson family cemetery.
In the decades since the 1973 death of her husband, Mrs. Johnson promoted environmental causes much as she had in the White House. On her 70th birthday, she and actress Helen Hayes founded the National Wildflower Research Center, later renamed for her. Into her 90s, she made occasional public appearances at the LBJ Library in Austin and at civic events.
Despite her achievements as first lady, the role did not come easily to the soft-spoken Mrs. Johnson.
"I feel as if I am suddenly on stage for a part I never rehearsed," she confided to a friend when the Johnsons moved into the White House after the Nov. 22, 1963, assassination of President John F. Kennedy.
She could not have found herself in a more chaotic theater. In addition to the grief and shock over the death of Kennedy, the nation was deeply divided over the civil rights movement and the Vietnam War.
But for the next five years, the woman who had stared down shyness most of her life gave a nearly flawless performance.
At a time when the South was fighting desegregation, Mrs. Johnson sweet-talked five Southern governors into joining her 1964 whistle-stop train tour from Washington to New Orleans to campaign for her husband, much reviled there for his support of civil rights.
"Her life was threatened by the Klan. She was jeered and booed. But she felt that civil rights was right, that it had to come," said Myra Gutin of Cherry Hill, a Rider University professor who interviewed Mrs. Johnson for The President's Partner, her 1989 book on first ladies.
And, as a political wife in the queasy era when the first stirrings of feminism were derisively dubbed "women's lib," Mrs. Johnson would greet the president at the end of his workday with the question: "Well, what did you do for women today?"
Her behind-the-scenes maneuvering to raise her husband's consciousness was typical. "It would not have been in character," Gutin said, "for her to be out front" the way Rosalynn Carter and Hillary Rodham Clinton later were.
Nor would it have been in character for President Johnson to let anyone steal his thunder. Almost from the minute Lady Bird and Lyndon Johnson met in Austin in 1934, while he worked as a secretary to U.S. Rep. Richard Kleberg (D., Texas), Johnson appeared to dominate the reserved young woman.
Claudia Alta Taylor - she was nicknamed as an infant when nurse Alice Tittle pronounced her new charge "as purty as a Lady Bird" - had just earned a journalism degree from the University of Texas and was back in Austin to visit college friends when one friend introduced her to Johnson.
On their first date, that September, he asked her to marry him. She thought it was a joke. But he kept asking, and soon gave her a diamond engagement ring.
On Nov. 17, 1934, he talked his reluctant fiancee into a wedding at St. Mark's Episcopal Church in San Antonio, where an equally reluctant minister watched as the couple argued their way into the church.
At the last minute, Lady Bird reminded Lyndon Johnson that they needed a wedding ring. A friend ran across the street to a Sears, Roebuck store, brought back a tray of rings so the couple could select the right size, and gave them the $2.50 band as a wedding present.
"I hope that marriage lasts," the minister reportedly said as the newlyweds left the church.
Little in the bride's background prepared her for the life her fiercely ambitious groom had in mind.
Claudia Taylor was born Dec. 22, 1912, in tiny Karnack, Texas, where her father ran a dry-goods store. Her mother died when she was 5, and she was raised mostly by an aunt.
She grew up surrounded by books, music and material comforts, but dressed plainly and was so shy that she was terrified of becoming valedictorian for fear of the speech she'd have to give. (At age 15, she graduated third in her class at Marshall High School.)
But within three years of her marriage, she found herself the wife of a congressman - Lyndon Johnson's first campaign was financed with $10,000 of her money - and was expected to hold her own in Washington's competitive social scene.
Slowly, painfully, she learned, at one point even taking public speaking lessons, to make her appearances easier, and dieting to a size more flattering to the stylish clothes her husband chose for her.
She also developed a keen business sense, parlaying a debt-ridden Austin radio station she bought for $31,000 in 1943 into a multimillion-dollar operation.
While Mrs. Johnson once described herself as "just a little mouse," Gutin recalled a woman who radiated "a certain sense of power that I didn't feel with any of the other first ladies" she met while working on her book.
But of course, Mrs. Johnson had had decades of practice coping with the powerful personality that was her husband. As imperious and demanding as he was, it was not unusual for him to belittle his wife's clothing, or rage at his staff.
"He did not spare the lash even when the target was his wife," wrote Robert A. Caro, the author of exhaustive biographies of Lyndon Johnson.
Again, Mrs. Johnson learned to cope. "She was the only one who could tell him to shut up," Gutin said. "He would fire people in a rage, just lose it, and she would go over to the people and say, 'Please understand that he works very hard and he didn't mean it. Come back to work tomorrow.' "
Mrs. Johnson learned to deal with another painful aspect of her husband's personality: his rumored infidelities. When the topic was raised in a television interview in 1987, she gave a graceful answer to an impossibly awkward question:
"You have to understand, my husband loved people. All people. And half the people in the world were women."
The Johnson daughters, Lynda Bird and Luci Baines, were teenagers when Lyndon Johnson became president. Each eventually married in the White House, the first weddings there in 50 years.
After Lyndon Johnson declined to run for reelection in 1968, the couple retired to the LBJ Ranch on the banks of the Pedernales River, about 60 miles west of Austin.
Their time at the ranch was a respite. They lived quietly, concentrating on projects such as his presidential library. Mrs. Johnson wrote one book, A White House Diary, and co-authored a second, Wildflowers Across America.
After her husband died of a heart attack in 1973, Mrs. Johnson concentrated on her interest in the environment, and served on presidential commissions. Her long list of honors included the Medal of Freedom in 1977 and the Congressional Gold Medal in 1988.
Surviving are her daughters, Lynda Johnson Robb and Luci Baines Johnson Turpin; seven grandchildren; a step-grandchild, and several great-grandchildren.
This article includes information from Inquirer wire services.