As of September 1, over 40,000 U.S. registered aircraft have been equipped to comply with the 2020 ADS-B Out mandate says the General Aviation Manufacturers Association (GAMA). The FAA estimates that 100,000 to 160,000 general aviation aircraft will need to comply with the mandate—or cease operations in ADS-B Out airspace.
Source: avwebOver 40,000 ADS-B Aircraft Operating in US