The numbers are a bit older, but https://fas.org/sgp/othergov/intel/clear-2012.pdf https://fas.org/sgp/othergov/intel/clear-2012.pdf claims there were 1.4 milli

The numbers are a bit older, but https://fas.org/sgp/othergov/intel/clear-2012.pdf https://fas.org/sgp/othergov/intel/clear-2012.pdf claims there were 1.4 millions top level clearances held in 2012.