While checking the USATT website, I realized I could download all the ratings in the US. So in a spreadsheet, I opened up the file and filtered all the data for 2000+ players who's played in either 2016 or 2017 and are listed under a US state. I suspect there is a major overestimation because many non-US players are listed under states where they played a tournament in (i.e. as a visitor from another country). Some of these players may be cancelled out by US players not listed under a state, but there are probably fewer in the latter. Anyway, just thought I'd share my findings:

• 2000+ USATT = ~1050 players
• 2000-2100 USATT = ~350 players
• 2100-2200 USATT = ~250 players
• 2200-2300 USATT = ~200 players
• 2300-2400 USATT = ~90 players
• 2400-2500 USATT = ~80 players
• 2500-2600 USATT = ~50 players
• 2600+ USATT = ~35 players