Joan lives in Portland. She was married to Bob Day, but they divorced when Jess was still a child. Despite the divorce, they have gotten together for post-divorce sex on multiple occasions, just for fun, mostly without their daughter's knowledge. She is happy and fun-loving like Jess, which contradicts Bob's more morose outlook on the world. She's not a big fan of Cece, who she seems to think corrupts her daughter - while Bob attended Cece's wedding to Shivrang at the end of season two, Joan did not.
In the series' "Pilot," Jess returns early from visiting her mother in Portland, hoping to surprise her boyfriend, Spencer. Unfortunately, she instead discovers that he's been cheating on her and promptly moves out of his home.
Later, Jess is talking to her mother on the phone, shortly after moving into the loft with Nick, Schmidt, and Coach. Even though she's watching Dirty Dancing, she promises her mother that she's not. When Nick walks through the living room, Jess says her mother wants to know if he's going to murder her when she's sleeping because he's a stranger she met on the Internet. Annoyed by the constant viewings of Dirty Dancing, and the endless crying in pyjamas on the couch, he says he is going to kill her, but Jess reports back to her mother that he said no.
- Held a grudge against Cece for wrecking her car for nearly 15 years. But even after discovering the truth, she still found a reason to dislike her, for reportedly giving Jess drugs.