Methods and apparatus to count people are disclosed. Example apparatus disclosed herein are to populate a list with first characteristic datasets obtained from a first plurality of images, respective ones of the first characteristic datasets representative of corresponding faces. Disclosed apparatus are also to perform comparisons of the first characteristic datasets to each other to determine a first number of unique faces, the comparisons limited to the first characteristic datasets obtained during the first period of time. Disclosed apparatus are further to delete the first characteristic datasets from the list after the first period of time has ended, and re-populate the list with second characteristic datasets obtained from a second plurality of images representative of the environment during a second period of time of the media presentation, the second period of time subsequent to the first period of time.