Mariclare Costello, the warm-hearted character actress who became a fixture in millions of American living rooms as the kindly schoolteacher Rosemary Hunter on CBS’ beloved family drama “The Waltons,” has died. She was 90.

Her family announced she died April 17, 2026, in Brooklyn. Though best remembered for her recurring role on “The Waltons,” her career stretched across six decades, from the stages of Broadway to cult horror cinema, prestige telefilms and Oscar-winning dramas.

From Peoria to the Bright Lights

The youngest of three sisters in a creativity-prizing family, Costello was born Feb. 3, 1936, in Peoria, Illinois. She studied at Clarke College in Iowa before pursuing a master’s degree in theater and education from Catholic University, where she trained in improvisation under the legendary Viola Spolin. During her years in Washington, she performed for President John F. Kennedy as Nerissa in a production of “The Merchant of Venice.”

Following graduate school, she relocated to New York City and joined the Lincoln Center Repertory Company as an original member while becoming a lifetime member of The Actors Studio. Theater became her first love. Her Broadway debut came in 1964 in Arthur Miller’s “After the Fall” opposite Jason Robards, launching a remarkable string of nine Broadway productions through 1970.

Those Broadway credits accumulated rapidly: “But For Whom Charlie” (1964), “The Changeling” (1964), “Tartuffe” (1965), “Danton’s Death” (1965), “The Country Wife” (1965), “Lovers and Other Strangers” (1968), “A Patriot for Me” (1969), and a 1970 revival of “Harvey” with James Stewart and Helen Hayes.

Hollywood and a Cult Horror Classic

Costello made her film debut in 1967’s “The Tiger Makes Out” alongside Eli Wallach and Anne Jackson. Television roles followed, but a low-budget 1971 horror film would secure her a permanent place in genre history.

In “Let’s Scare Jessica to Death,” she portrayed Emily, a free-spirited hippie who joins Jessica (Zohra Lampert) and her husband before revealing herself as a vampire. Costello’s undead character rising slowly from a misty lake became one of the most haunting images in 1970s horror, with the film achieving cult status over the decades.

She continued building an impressive screen résumé, playing the wife of Martin Sheen’s title character in the acclaimed 1974 telefilm “The Execution of Private Slovik.” In 1980, she appeared in Robert Redford’s Oscar-winning “Ordinary People” as the sympathetic sister-in-law of Mary Tyler Moore’s grieving mother.

Walton’s Mountain and a Lasting Legacy

For TV audiences, Costello became best known as Miss Rosemary Hunter, the gentle Walton’s Mountain schoolteacher who recognized young John-Boy Walton’s literary talent and encouraged him to pursue writing. She appeared in the role across five seasons of “The Waltons” between 1972 and 1977, and her character eventually married Rev. Matthew Fordwick, the town’s preacher, portrayed by John Ritter before his “Three’s Company” fame.

She led the cast of CBS’s “The Fitzpatricks” as the family matriarch in 1977, a single-season drama. Her episodic television work throughout the 1970s, ’80s and ’90s included “Ironside,” “Kojak,” “Little House on the Prairie,” “Lou Grant,” “Murder, She Wrote,” “Santa Barbara,” “Chicago Hope,” “Judging Amy” and “Providence.”

A Life Beyond the Screen

She met Allan Arbus, the “M*A*S*H” actor who became her husband, in an acting class taught by Mira Rostova. The pair fell in love while rehearsing a Dorothy Parker play, marrying in 1977 and staying together until his death in 2013.

Family and friends recalled her as a teacher, mentor, wonderful cook and animal lover whose curiosity touched every aspect of her existence. “She was also, in every dimension of her life, someone who paid attention,” her family wrote. “She could talk to anyone, was interested in everything, and was a relentless asker of questions.”

She is survived by her daughter, stage director Arin Arbus, and Arin’s partner, playwright Ethan Lipton; her granddaughter, Bird; and stepdaughters Amy and Doon. A funeral service will be held in New York City, with burial and a remembrance to follow in her hometown of Peoria.