The cast of the show's second season include Tim Robbins, Lizzy Caplan and Elsie Fisher. Robbins plays Reginald "Pop" Merrill, a character from King's 1990 novella The Sun King who is the head of a crime family and dying of cancer. Paul Sparks (House of Cards, Boardwalk Empire) plays Merrill's nephew, John, a bully who is slated to take over his business. Matthew Alan (13 Reasons Why) plays Merrill's brother, who struggles to keep the peace.

Yusra Warsama (Call the Midwife) plays a doctor who runs a rural hospital and finds herself facing a supernatural test. The doctor's brother, played by Barkhad Abdi (Captain Phillips), is tasked with running a Somalian community center. Lizzy Caplan plays Annie Wilkes, a crazed nurse from King's 1987 novel Misery, and Elsie Fisher plays her homeschooled teenage daughter.

The second season of Castle Rock will consist of ten episodes. Just in time for Halloween, the show joins Hulu's lineup of horror shows scheduled to premiere in the fall, including Light as a Feather and Into the Dark: Pure.