This article traces the sources of the estimates of the number of American Sign Language users in the United States. A variety of claims can be found in the literature and on the Internet, some of which have been shown to be unfounded but continue to be cited. In our search for the sources of the various (mis)understandings, we have found that all of the data-based estimates of the number of people who use ASL in the United States have their origin in a single study published in the early 1970s, which inquired about signing in general and not ASL use in particular. There has been neither subsequent research to update these estimates nor any specific study of ASL use. The article concludes with a call to action to rectify this problem. (Contains 2 tables and 1 note.)