She died in Tampa.

https://www.imdb.com/name/nm0247659/

From her son, John:
https://m.facebook.com/groups/officialnightofthelivingdead/posts/1962303913918043/

https://m.youtube.com/watch?v=05io_0b_J_k
(short tribute)

And:

https://bloody-disgusting.com/news/3679539/r-p-night-living-dead-actress-marilyn-eastman-passed-away/

Sad news today, as we’ve learned that another member of George A. Romero’s Night of the Living Dead family has passed away. The George A. Romero Foundation has this morning confirmed reports that Marilyn Eastman, who played Helen Cooper in the original 1968 classic, has passed away at the age of 87.

The foundation tweets, “It is with great sadness that we can confirm the passing of Marilyn Eastman on 8/22/21. Please join us in wishing her family peace at this painful time.”

In addition to starring in Romero’s Night of the Living Dead, Marilyn Eastman was also an integral figure behind the scenes of the independent production, working in the makeup, prop, and sound departments, as well as helping to edit the film’s screenplay. Eastman also appears in the film as a zombie, pulling double duty as an actress in the legendary classic.

Additionally, Marilyn Eastman, along with fellow Night of the Living Dead star Karl Hardman, was a founding member of the film’s production company, Image Ten Productions.

“Godspeed, Marilyn. Give our love to Karl,” The George A. Romero Foundation tweeted this morning. Karl Hardman had passed away back in September 2007, at the age of 80.

There are several people Night of the Living Dead would simply not exist without, and Marilyn Eastman was one of them. We send our deepest condolences to Marilyn’s family and friends.

It is with great sadness that we can confirm the passing of Marilyn Eastman on 8/22/21. Please join us in wishing her family peace at this painful time.
Godspeed, Marilyn. Give our love to Karl. 💔 pic.twitter.com/qBidxsEIW3

— The George A. Romero Foundation (@theGARFofficial) August 23, 2021