Mariclare Costello, the veteran stage and screen actress best known for her role as Rosemary Hunter on The Waltons and her appearance in the cult horror film Let’s Scare Jessica to Death, died April 17, 2026, in Brooklyn, New York. She was 90.

According to her obituary, she was born Mariclare Catherine Costello Arbus in 1936 in Peoria, Illinois. Mariclare was the youngest of three sisters in a family that valued creativity and craftsmanship. Her mother worked in state government and had a passion for restoring antiques, while her father was a civil engineer. That appreciation for beauty and detail would shape Costello’s life and work.

She attended schools in Peoria before studying at Clarke College in Iowa and spending a formative year at the University of Vienna. She later earned a master’s degree in theater and education from Catholic University, where she studied improv under Viola Spolin and performed for President John F. Kennedy in a production of The Merchant of Venice.

Costello moved to New York City to pursue acting, building a respected career in theater. She performed at major institutions including the Public Theater and was a lifetime member of the Actors Studio. As part of the Lincoln Center Repertory Company, she worked alongside notable figures such as Jerome Robbins, Faye Dunaway and James Earl Jones. She originated a role in Arthur Miller’s After the Fall, opposite Jason Robards, directed by Elia Kazan, and appeared on Broadway in Harvey with Jimmy Stewart.

Per People, Mariclare Costello appeared in multiple early episodes of The Waltons, where her portrayal of teacher Rosemary Hunter became a memorable part of the show.

After relocating to Los Angeles in the late 1960s, she expanded into film and television, including a role in the Emmy-winning telefilm The Execution of Private Slovik. Her TV résumé also included a leading role on The Fitzpatricks and guest appearances on series such as Kojak, Lou Grant, Murder, She Wrote, Chicago Hope, Judging Amy and Providence.

On the film side, her credits included Ordinary People and The Adventures of Buckaroo Banzai Across the 8th Dimension.

Costello was married to actor Allan Arbus — known for his role on M*A*S*H — from 1977 until his death in 2013. The two met in an acting class led by Mira Rostova and developed a relationship while rehearsing a Dorothy Parker play before eventually settling together in Los Angeles.

Later, while raising her daughter in Los Angeles, Costello devoted herself to teaching and directing. She led drama programs at schools including Loyola High School and Loyola Marymount University, and worked with community organizations such as Homeboy Industries.