- "Eleven, including me. Five boys, six girls, four parents, two drivers, and a partridge in a pear tree."
- ―Heather to Kate
Heather McCallister is Kevin's oldest cousin. She attends Northwestern University, and her mom and dad, Georgette and Rob live in Paris as Rob had gotten a job transfer the summer before. She has twin younger sisters and a younger brother whose names are Liz, Mickey, and Josh. She tags along with the other McCallisters for the trip to Paris. She is portrayed by Kristin Minter.
She first appears at the beginning of the film asking her cousin Tracy if she ordered the pizza to which Tracy tells her that Buzz did. She also tells Harry that her parents are in Paris after asking if they are there. Heather is later seen eating pizza in the kitchen and gets mad at Kevin along with the others after Kevin causes an incident. The next day as the family is preparing to leave Kate tells Heather to count heads to make sure everyone is in the vans which she does and accidentally mistakes a neighborhood kid named Mitch Murphy for Kevin and they leave without him. In Paris, as Kate is trying to make a phone call to the Chicago Police, Heather looks worried about Kevin being accidentally left behind at home (and also guilty as she was the one who miscounted), and tries to make a phone call to someone in Chicago who can go check on Kevin to no avail. Heather later goes to her parents' apartment with her Uncle Frank, Aunt Leslie, Uncle Peter, and her cousins while her Aunt Kate tries to get a flight to Chicago. Heather is last seen in her parents' apartment helping her dad and her brother decorate the Christmas Tree.
- The McCallisters are lucky that they did not lose any other children since Heather counted herself twice and forgot to count Linnie.
- "Eleven. Including me. Five boys, six girls, four parents, two drivers...and a partridge in a pear tree".