Johni Cerny, the chief genealogist for the PBS series “Finding Your Roots,” who helped some 200 famous people — among them Oprah Winfrey, Quincy Jones, Senator Bernie Sanders and Speaker Nancy Pelosi — trace their ancestry, died on Wednesday in Lehi, Utah, near Salt Lake City. She was 76.

Deborah Christensen, Ms. Cerny’s partner of 23 years, said the cause was coronary artery disease and congestive heart failure.

“Johni Cerny was the proverbial dean of American genealogical research,” Henry Louis Gates Jr., the Harvard professor who is a host and executive producer of “Finding Your Roots,” said in a statement. In an email message on Thursday, he described her work as “transforming raw data into narratives and metaphors about diversity and our common humanity.”

Ms. Cerny’s passion for the field began in childhood, for intensely personal reasons.

Jonnette Elaine Cerny was born on Aug. 27, 1943, in Kansas City, Mo. Her mother was Vivian Elaine (West) Cerny, and the man she was told was her father was John Steve Cerny, a soldier in World War II who later worked in the heating and air-conditioning business. She was the oldest of five children.

The family later moved to Southern California. She enrolled at the University of Missouri but transferred to Brigham Young University in Utah, where she received a bachelor’s degree in social work and genealogical research in 1969.

She was always fascinated by family trees. Her maternal grandmother, Bertha Smith West, had been adopted and always wanted to learn the identity of her biological parents. Johni was 19 when she began that research, but it was not until long after her grandmother’s death in 1972 that she was able to use DNA — essentially a 21st-century genealogical tool — to find their names.

Meanwhile, Ms. Cerny had long suspected that John Cerny was not her biological father. It was not until 2018, however, that with the help of DNA she was able to identify the man who was: Charles Owen Williams.

According to Nick Sheedy, a researcher at Lineages, Ms. Cerny’s family history and genealogical research company, he and Ms. Cerny signed up with “every database out there” and the process took about nine months.

Mr. Williams had died in 1960, but Ms. Cerny soon met a whole new circle of relatives on her father’s side.

Ms. Cerny did not go into genealogical research immediately after college. From 1972 to 1979 she served in the Army, reaching the rank of captain. She returned to Utah because of its research resources, particularly the Church of Jesus Christ of Latter-day Saints’ Family History Library.

She founded Lineages in 1983, before most computerized databases and long before $99 mail-order DNA reports. As a social media tribute to her observed, she spent a lot of time “looking through microfilm and toting bags of quarters for the copy machines.”

Ms. Cerny was an editor and author of “The Source: A Guidebook of American Genealogy” (1984) and “The Library: A Guide to the LDS Family History Library” (1986). A favorite research subject of hers was Germanna, the Virginia settlement of Germans who in 1718 were tricked into indentured servitude. She and Gary J. Zimmerman published several “Before Germanna” books, including histories of the Baumgartner, Dieter, Moyer and Willheit families.

She began working on PBS projects with Professor Gates in 2006 as a researcher on “African American Lives,” which Virginia Heffernan, in a review in The New York Times, called “the most exciting and stirring documentary on any subject to appear on television in a long time.” Ms. Cerny also worked on “Faces of America” (2010) and “The African Americans: Many Rivers to Cross” (2013).

From 2012 through 2019, she was the chief researcher for “Finding Your Roots.” Her subjects on that series also included Stephen Colbert, Larry David, Queen Latifah, Representative John Lewis, Meryl Streep and Tina Turner.

Ms. Cerny was never one to pinpoint a favorite project, associates said, but in a 2019 interview she mentioned an episode with the comedian Sarah Silverman.

“Her comment just took the words right out of my mouth,” Ms. Cerny said. “She was looking at a photograph of family members she had never seen before. And she just said, ‘I wish I could crawl into this picture and know what’s going on in there.’”

In addition to Dr. Christensen, a psychologist, Ms. Cerny is survived by a brother, Jack Cerny, and three sisters, Antoinette Greenstone, Nanette Muirhead and Stevette Shinkle. She helped raise Dr. Christensen’s sons, Tim, Matthew and Jake, and her daughters, Anna Ward and Rachel Stowe. There are 11 grandchildren.

There was little doubt that Ms. Cerny loved her career. In a 2019 video, she admitted to a workday that began around 7:30 a.m. and ended at about 6:30 p.m. — and to a habit of waking up in the middle of the night with an idea and going straight to her computer. Her work, she said, was “very addictive.”