Given the high levels of congestion that many commuters in the United States experience, the urban air mobility community has been exploring the potential of using a new class of electric vertical takeoff and landing (eVTOL) aircraft for commuters. To date, only a few studies have been conducted that compare how potential air taxi demand across cities varies. This study calculates a measure of air taxi demand for commuters for the 40 most populous combined statistical areas (CSAs) in the U.S. by using: (1) cell phone data to identify regular commuters in cities, (2) census data to associate household income characteristics with commuters, and (3) a mode choice model calibrated from a stated preference survey to predict the number of commuters that would use an air taxi. Air taxi commuter demand is concentrated in a handful of CSAs; the CSAs for New York City, Los Angeles, and Washington, D.C., generate 33 percent of the overall air taxi demand. Results are sensitive to location of existing vertiports, existing ground infrastructure and congestion levels on competing modes, and current commute patterns. A resultant set of online maps of potential air taxi routes allows readers to visualize how air taxi commuter routes differ across CSAs. Results will be of value both to aircraft manufacturers seeking to design air taxi vehicles to serve different cities as well as city planners for identifying where investments in port infrastructure may be needed to support a commuter air taxi service.