The date has long held significance for fans of the sci-fi movies as a pun on the franchise's popular line, "May the force be with you."
So to mark the occasion on Saturday, the 26-year-old shared a photo of herself with her mother, who died in December 2016 at the age of 60. In the snap, Carrie and Billie made serious faces for the camera as they both held their hands up to their chest.
The "Scream Queens" star captioned the post by spelling out "May The Fourth" in emojis.
Carrie was flying from London to Los Angeles on December 23, 2016, when she went into cardiac arrest. Paramedics removed her from the flight and rushed her to a nearby Los Angeles hospital, where she was treated for a heart attack. She died in the hospital four days later.
The much-loved actress played Princess Leia in the original movies alongside Harrison Ford and Mark Hamill, and reprised her role for the sequels with Daisy Ridley, John Boyega and Oscar Isaac as General Leia Organa.
Earlier this week, Billie paid tribute to Peter Mayhew, the actor who portrayed the beloved Chewbacca in "Star Wars", after his death on Thursday.
Sharing a never-before-seen collection of photos of her mother with Peter, Billie captioned the post with a simple red heart.
In March, "Star Wars" director J.J. Abrams confirmed that Carrie will appear in "Star Wars: The Rise of Skywalker", three years after her unexpected death.
Billie will also be in the film, reprising her role as Lieutenant Connix.