FAA released some location data about their sUAS owner registry. This registry is intended for owners of model aircraft, rc helicopters, and multirotors (Collectively known as Small Unmanned Aerial Systems, or "Drones"). As other websites have noted, the registrations appear to follow population centers, which makes sense.
With nearly half a million registered drone owners, you can't help but wonder how many owners have opted not to register. 3D Robotics, America's largest drone manufacturer, estimates half a million have been sold in the US alone. Dronelife.com did some math (and guestimating), and came up with even more. At the end of the day, drones are easy enough to build that we will never truly know the total number of drones in the US.
If the FAA does a similar release in the future, I'd love to do a comparison of that data to the original, and see how registration has grown over time.