Less than 4,000 if you're only talking about retail. Quora thinks 715,000 retail establishments, of which 315k with less than 5 employees so round 'bout 300k retail firms of any size. $3.8T in sales, 15m employees. Not sure what the point is here but there's the numbers.
I'm thinking that the numbers we use to measure the health of our economy are only looking at publicly traded companies. At some point - now? soon? next year? ten years? - publicly traded companies will not be the majority of the economy, and therefore will be poor indicators of America's economic health. In fact, looking at the list of the top 10 privately held companies, I'd argue that we may be at that point now. The US economy is worth about $18 trillion dollars, and privately held companies are worth about $5 trillion today. That means that 27% of our current economic activity is not represented in the graphs you presented earlier in this thread. (And in the data used by economists and government officials to measure the health of the US economy.) How do we improve our measurements and forecasting, if 27% of the money flowing around our economy is not measured/tracked like it is for publicly traded companies? How valuable are our current measurements, and how long can we pretend they are meaningful when they fail to account for such a large portion of our GDP? Not sure what the point is here but there's the numbers.