Which J.K. Rowling novel was her first book written for adults?

The Casual Vacancy was J.K. Rowling’s first novel written for adults.

Little, Brown published the novel on 27 September 2012. It is set in the fictional English town of Pagford and begins after the unexpected death of parish councillor Barry Fairbrother.

Unlike the Harry Potter books, The Casual Vacancy is a contemporary social novel about class, local politics, family conflict, poverty, and tensions between communities. Its plot follows many residents rather than one central young hero, giving the book a deliberately broad ensemble structure.

The novel is sometimes confused with Rowling’s later crime fiction because both were marketed outside the Harry Potter series. The Cormoran Strike books, however, were published under the Robert Galbraith pen name and began with The Cuckoo’s Calling in 2013.