- "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 McCallister if she ordered the pizza to which Tracy tells her that Buzz did. She also tells Harry that her Mom and Dad live in Paris after he asks her if they're 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 to which does and accidentally mistakes a neighborhood kid named Mitch Murphy as 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 accidently 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 with no luck. Heather later goes to her parents' apartment with her Uncle Frank, Aunt Leslie, her 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.
- "Eleven. Including me. Five boys, six girls, two drivers... and a partridge in a pear tree".