In "The Boogeyman," JJ reveals that she is afraid of the woods. When agents Derek Morgan and Spencer Reid ask her why, she tells them a chilling story about working as a summer camp counselor and discovering her boss' murdered body in his cabin. After telling the story, she admits she was joking, and says she doesn't know why she is afraid of the woods. In the same episode, JJ also states that she has a niece who, at the time, is about 8 years old. However, the canonicity of this statement is unknown, as only one sibling of JJ’s is ever mentioned, her long dead sister, Rosalyn. It could be that this niece is related to her long-term partner Will, but it is never stated that he has siblings.