Jo was born to and on April 7, 1985 as the couple's only child. Because she lived at , Jo grew up around hunters, including and , whom she and her parents regarded as family. She called the hunters she knew "uncle", such as Uncle Shawn.
On Jo's eighth birthday, Bill gave her a bow-and-arrow set and taught her how to use it, while Ellen gave her a diary to write in, which she later turned into a hunter's journal. Jo ends up meeting Jacob and his twin sister Claire at the Roadhouse though Jo swears she had seen them before but she couldn't recall so she asks them if they are related to John Winchester and Jacob said yes and that is his and Claire's uncle. When Jo met Jacob she started developing feelings for him and Ellen was really surprised that Jo ended up falling in love with Jacob.
- Jacob Winchester. (best friend/crush/husband): Jo befriends Jacob when she first meets him though she tells Claire that she is in love with him and wants to be with him. After Jacob divorced Ruby he went to Jo and then Jo ran up to Jacob and hugged him. They get married after three months of dating. Jo really loves her husband and doesn't want to lose him. She made a custom lever action shotgun for Jacob.
- Claire Winchester (best friend/sister-in-law): Jo and Claire are best friends.